Doc for contributing guidelines

.github/PULL_REQUEST_TEMPLATE.md

@@ -23,3 +23,21 @@ If `Refactor`, describe the new or existing tests that verify no behavior was ch
 ## New behavior tests
 
 If `Feature` or `Fix`, describe the new or existing tests that verify the new behavior is correct and expected.
+
+## Versioning Implications
+
+- [ ] This PR will affect [semantic versioning as defined for ICS](../CONTRIBUTING.md#semantic-versioning)
+
+If the above box is checked, which version should be bumped?
+
+- [ ] `MAJOR`: Consensus breaking changes to both the provider and consumers(s), including updates/breaking changes to IBC communication between provider and consumer(s)
+- [ ] `MINOR`: Consensus breaking changes which affect either only the provider or only the consumer(s)
+- [ ] `PATCH`: Non consensus breaking changes
+
+## Targeting
+
+Please select one of the following:
+
+- [ ] This PR is only relevant to main
+- [ ] This PR is relevant to main, and should also be back-ported to ____ (ex: v1.0.0 and v1.1.0)
+- [ ] This PR is only relevant to ____ (ex: v1.0.0, v1.1.0, and v1.2.0)

CONTRIBUTING.md

@@ -0,0 +1,74 @@
+# Contributing
+
+- [Contributing](#contributing)
+  - [Architecture Decision Records (ADR)](#architecture-decision-records-adr)
+  - [PR Targeting](#pr-targeting)
+  - [Development Procedure](#development-procedure)
+  - [Semantic Versioning](#semantic-versioning)
+  - [Testing](#testing)
+  - [Protobuf](#protobuf)
+
+Thank you for considering making contributions to Interchain Security (ICS)!
+
+To contribute, you could start by browsing [new issues](https://github.com/cosmos/interchain-security/issues).
+
+## Architecture Decision Records (ADR)
+
+When proposing an architecture decision for ICS, please start by opening an [issue](https://github.com/cosmos/interchain-security/issues/new/choose) with a summary of the proposal. Once the proposal has been discussed and there is rough alignment on a high-level approach to the design, you may either start development, or write an ADR.
+
+If your architecture decision is a simple change, you may contribute directly without writing an ADR. However, if you are proposing a significant change, please include a corresponding ADR.
+
+In certain circumstances, the architecture decision may require changes to the ICS spec. Note that the spec is responsible for defining language-agnostic, implementation-agnostic behaviors for the ICS protocol. Whereas ADRs are responsible for communicating implementation decisions contained within this repo.
+
+To create an ADR, follow the [template](https://github.com/cosmos/interchain-security/blob/main/docs/architecture/adr-template.md) and [doc](https://github.com/cosmos/interchain-security/blob/main/docs/architecture/README.md). If you would like to see examples of how these are written, please refer to the current [ADRs](https://github.com/cosmos/interchain-security/tree/main/docs/architecture).
+
+### ADR Proposals
+
+Architecture Decision Records (ADRs) may be proposed by any contributors or maintainers of ICS. ADRs are intended to be iterative, and may be merged into `main` while still in a `Proposed` status
+
+## PR Targeting
+
+ICS adheres to the [trunk based development branching model](https://trunkbaseddevelopment.com/).
+
+All feature additions and all bug fixes must be targeted against `main`. Exception is for bug fixes which may only be relevant to a previously released version. In that case, the bug fix PR must target against the release branch.
+
+If needed, we will backport a commit from `main` to a release branch with appropriate consideration of versioning.
+
+## Development Procedure
+
+- The latest state of development is on `main`
+- `main` must never fail `make test`
+- Create a branch or fork the repo to start work
+- Once development is completed, or during development as a draft, you may open a pull request. The pull request description should follow the [default template](./.github/PULL_REQUEST_TEMPLATE.md). Note that a PR can be of one or multiple types, including `Feature`, `Fix`, `Refactor`, `Testing`, and `Docs`. Please try to minimize the number of categories that you could classify a single PR as.
+- It's notable that your PR may have versioning implications. See [Semantic Versioning](#semantic-versioning) for more information
+- Code is squash merged through the PR approval process
+
+## Semantic Versioning
+
+ICS uses a variation of [semantic versioning](https://semver.org/).
+
+Note that state breaking changes are a subset of consensus breaking changes. Therefore we'll only refer to the latter when talking about versioning.
+
+ICS is a distributed, IBC based protocol in which multiple blockchains could be affected by a version bump. Therefore incrementing a MAJOR version number indicates that the PR updates, or is a breaking change to the way that the provider and consumer(s) communicate with one another over IBC. If a PR is consensus breaking to both the provider and consumer(s), then it requires a MAJOR version bump.
+
+Incrementing a MINOR version number indicates that a PR is only consensus breaking to the provider, or only to the consumers, where IBC communication remains unchanged.
+
+Incrementing a PATCH version number indicates that a PR is not consensus breaking to the provider or consumers. This could include node API changes, or other miscellaneous and often rare changes.
+
+Pure documentation, testing, and refactoring PRs do not require a version bump.
+
+### Backwards Compatibility
+
+A MAJOR version of ICS will always be backwards compatible with the previous MAJOR version of ICS. Versions before that are not supported. For example, a provider chain could run ICS at version 3.4.5, and would be compatible with consumers running ICS at 2.0.0, 2.1.2, 3.2.1, but not 1.2.7.
+
+## Testing
+
+Appropriate tests should be written with a new feature, and all existing tests should pass. See [docs/testing.md](./docs/testing.md) for more information.
+
+## Protobuf
+
+We use [Protocol Buffers](https://developers.google.com/protocol-buffers) along with [gogoproto](https://github.com/gogo/protobuf) to generate code for use in ICS.
+
+For determinstic 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.
+
+To generate the protobuf stubs, you can run `make proto-gen`.