Add Developer's guide and best practices (CosmWasm#1075)

* Add Developer's guide and best practices

* Fix comments

CODING_GUIDELINES.md

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+# Coding Guidelines
+
+This document is an extension to [CONTRIBUTING](./CONTRIBUTING.md) and provides more details about the coding guidelines and requirements.
+
+## API & Design
+
+* Code must be well structured:
+    * packages must have a limited responsibility (different concerns can go to different packages),
+    * types must be easy to compose,
+    * think about maintainbility and testability.
+* "Depend upon abstractions, [not] concretions".
+* Try to limit the number of methods you are exposing. It's easier to expose something later than to hide it.
+* Follow agreed-upon design patterns and naming conventions.
+* publicly-exposed functions are named logically, have forward-thinking arguments and return types.
+* Avoid global variables and global configurators.
+* Favor composable and extensible designs.
+* Minimize code duplication.
+* Limit third-party dependencies.
+
+Performance:
+
+* Avoid unnecessary operations or memory allocations.
+
+Security:
+
+* Pay proper attention to exploits involving:
+    * gas usage
+    * transaction verification and signatures
+    * malleability
+    * code must be always deterministic
+* Thread safety. If some functionality is not thread-safe, or uses something that is not thread-safe, then clearly indicate the risk on each level.
+
+## Best practices
+
+* Use [goimports](https://pkg.go.dev/golang.org/x/tools/cmd/goimports) as your code formatter.
+
+* Always wrap returned errors. 
+    * Doing `if err != nil { return err }` does not include each callers' context. Pushing errors up the stack without context makes it harder to test and debug. Additionally, a short context description makes it easier for the reader to understand the code. Example:
+
+        ```go
+        if !coins.IsZero() { 
+            if err := k.bank.TransferCoins(ctx, caller, contractAddress, coins); err != nil { 
+                return nil, err 
+            } 
+        } 
+        ```
+
+    * It would be an improvement to return  `return nil, sdkerror.Wrap(err, "lock contract coins")`
+    * Please notice that fmt.Errorf is not used, because the error handling predates fmt.Errorf and errors.Is 
+
+* Limit the use of aliases, when not used during the refactoring process.

CONTRIBUTING.md

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+# Contributing
+
+Thank you for considering making contributions to Wasmd!
+
+Contributing to this repo can mean many things, such as participating in
+discussion or proposing code changes. To ensure a smooth workflow for all
+contributors, the general procedure for contributing has been established:
+
+1. Start by browsing [new issues](https://github.com/CosmWasm/wasmd/issues).
+   * Looking for a good place to start contributing? How about checking out some [good first issues](https://github.com/CosmWasm/wasmd/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22) or [bugs](https://github.com/CosmWasm/wasmd/issues?q=is%3Aopen+is%3Aissue+label%3Abug)?
+2. Determine whether a GitHub issue or discussion is more appropriate for your needs:
+   1. If the issue you want addressed is a specific proposal or a bug, then open a [new issue](https://github.com/CosmWasm/wasmd/issues/new).
+   2. Review existing [issues](https://github.com/CosmWasm/wasmd/issues) to find an issue you'd like to help with.
+3. Participate in thoughtful discussion on that issue.
+4. If you would like to contribute:
+   1. Ensure that the proposal has been accepted.
+   2. Ensure that nobody else has already begun working on this issue. If they have,
+      make sure to contact them to collaborate.
+   3. If nobody has been assigned for the issue and you would like to work on it,
+      make a comment on the issue to inform the community of your intentions
+      to begin work.
+5. To submit your work as a contribution to the repository follow standard GitHub best practices. See [pull request guideline](#pull-requests) below.
+
+**Note:** For very small or blatantly obvious problems such as typos, you are
+not required to an open issue to submit a PR, but be aware that for more complex
+problems/features, if a PR is opened before an adequate design discussion has
+taken place in a GitHub issue, that PR runs a high likelihood of being rejected.
+
+## Development Procedure
+
+* The latest state of development is on `main`.
+* `main` must never fail `make lint test test-race`.
+* No `--force` onto `main` (except when reverting a broken commit, which should seldom happen).
+* Create a branch to start work:
+    * Fork the repo (core developers must create a branch directly in the Wasmd repo),
+    branch from the HEAD of `main`, make some commits, and submit a PR to `main`.
+    * For core developers working within the `wasmd` repo, follow branch name conventions to ensure a clear
+    ownership of branches: `{issue#}-branch-name`.
+    * See [Branching Model](#branching-model-and-release) for more details.
+* Be sure to run `make format` before every commit. The easiest way
+  to do this is have your editor run it for you upon saving a file (most of the editors
+  will do it anyway using a pre-configured setup of the programming language mode).
+* Follow the [CODING GUIDELINES](CODING_GUIDELINES.md), which defines criteria for designing and coding a software.
+
+Code is merged into main through pull request procedure.
+
+### Testing
+
+Tests can be executed by running `make test` at the top level of the wasmd repository.
+
+### Pull Requests
+
+Before submitting a pull request:
+
+* merge the latest main `git merge origin/main`,
+* run `make lint test` to ensure that all checks and tests pass.
+
+Then:
+
+1. If you have something to show, **start with a `Draft` PR**. It's good to have early validation of your work and we highly recommend this practice. A Draft PR also indicates to the community that the work is in progress.
+   Draft PRs also helps the core team provide early feedback and ensure the work is in the right direction.
+2. When the code is complete, change your PR from `Draft` to `Ready for Review`.
+3. Be sure to include a relevant changelog entry in the `Unreleased` section of `CHANGELOG.md` (see file for log format). The entry should be on top of all others changes in the section.
+
+PRs name should start upper case.
+Additionally, each PR should only address a single issue.
+
+NOTE: when merging, GitHub will squash commits and rebase on top of the main.
+
+## Protobuf
+
+We use [Protocol Buffers](https://developers.google.com/protocol-buffers) along with [gogoproto](https://github.com/cosmos/gogoproto) to generate code for use in Wasmd.
+
+For deterministic behavior around Protobuf tooling, everything is containerized using Docker. Make sure to have Docker installed on your machine, or head to [Docker's website](https://docs.docker.com/get-docker/) to install it.
+
+For formatting code in `.proto` files, you can run `make proto-format` command.
+
+For linting we use [buf](https://buf.build/). You can use the commands `make proto-lint` to lint your proto files.
+
+To generate the protobuf stubs, you can run `make proto-gen`.
+
+We also added the `make proto-all` command to run all the above commands sequentially.
+
+In order for imports to properly compile in your IDE, you may need to manually set your protobuf path in your IDE's workspace settings/config.
+
+For example, in vscode your `.vscode/settings.json` should look like:
+
+```json
+{
+    "protoc": {
+        "options": [
+        "--proto_path=${workspaceRoot}/proto",
+        ]
+    }
+}
+```
+
+## Branching Model and Release
+
+User-facing repos should adhere to the trunk based development branching model: https://trunkbaseddevelopment.com. User branches should start with a user name, example: `{moniker}/{issue#}-branch-name`.
+
+Wasmd utilizes [semantic versioning](https://semver.org/).
+
+### PR Targeting
+
+Ensure that you base and target your PR on the `main` branch.
+
+All feature additions and all bug fixes must be targeted against `main`. Exception is for bug fixes which are only related to a released version. In that case, the related bug fix PRs must target against the release branch.
+
+If needed, we backport a commit from `main` to a release branch (excluding consensus breaking feature, API breaking and similar).