Add README to project root (#1253)

* Added root README.md draft

* Modified Contribution section to reflect unified guidelines

* Update README.md

Co-authored-by: Squirrel <gilescope@gmail.com>

* Expand Substrate description

* Added Badges and Upstream deps

* Fixed badge links

* Fixed CONTRIBUTING.md links, added security and resources section to root README.md

* Moved runtimes link to Polkadot section

---------

Co-authored-by: Squirrel <gilescope@gmail.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

README.md

@@ -0,0 +1,56 @@
+> NOTE: We have recently made significant changes to our repository structure. In order to 
+streamline our development process and foster better contributions, we have merged three separate 
+repositories Cumulus, Substrate and Polkadot into this repository. Read more about the changes [
+here](https://polkadot-public.notion.site/Polkadot-SDK-FAQ-fbc4cecc2c46443fb37b9eeec2f0d85f).
+
+# Polkadot SDK
+
+![](https://cms.polkadot.network/content/images/2021/06/1-xPcVR_fkITd0ssKBvJ3GMw.png)
+
+[![StackExchange](https://img.shields.io/badge/StackExchange-Community%20&%20Support-222222?logo=stackexchange)](https://substrate.stackexchange.com/)
+
+The Polkadot SDK repository provides all the resources needed to start building on the Polkadot 
+network, a multi-chain blockchain platform that enables different blockchains to interoperate and 
+share information in a secure and scalable way. The Polkadot SDK comprises three main pieces of 
+software:
+
+## [Polkadot](./polkadot/)
+[![PolkadotForum](https://img.shields.io/badge/Polkadot_Forum-e6007a?logo=polkadot)](https://forum.polkadot.network/) [![Polkadot-license](https://img.shields.io/badge/License-GPL3-blue)](./polkadot/LICENSE)
+
+Implementation of a node for the https://polkadot.network in Rust, using the Substrate framework. 
+This directory currently contains runtimes for the Polkadot, Kusama, Westend, and Rococo networks. 
+In the future, these will be relocated to the [`runtimes`](https://github.com/polkadot-fellows/runtimes/) repository.
+
+## [Substrate](./substrate/)
+ [![SubstrateRustDocs](https://img.shields.io/badge/Rust_Docs-Substrate-24CC85?logo=rust)](https://paritytech.github.io/substrate/master/substrate/index.html) [![Substrate-license](https://img.shields.io/badge/License-GPL3%2FApache2.0-blue)](./substrate/README.md#LICENSE)
+
+Substrate is the primary blockchain SDK used by developers to create the parachains that make up 
+the Polkadot network. Additionally, it allows for the development of self-sovereign blockchains 
+that operate completely independently of Polkadot.
+
+## [Cumulus](./cumulus/)
+[![CumulusRustDocs](https://img.shields.io/badge/Rust_Docs-Cumulus-222222?logo=rust)](https://paritytech.github.io/cumulus/cumulus_client_collator/index.html) [![Cumulus-license](https://img.shields.io/badge/License-GPL3-blue)](./cumulus/LICENSE)
+
+Cumulus is a set of tools for writing Substrate-based Polkadot parachains.
+
+## Upstream Dependencies
+
+Below are the primary upstream dependencies utilized in this project:
+
+- [parity-scale-codec](https://crates.io/crates/parity-scale-codec)
+- [parity-db](https://crates.io/crates/parity-db)
+- [parity-common](https://github.com/paritytech/parity-common)
+- [trie](https://github.com/paritytech/trie)
+
+## Security
+
+The security policy and procedures can be found in [docs/SECURITY.md](./docs/SECURITY.md).
+
+## Contributing & Code of Conduct
+
+Ensure you follow our [contribution guidelines](./docs/CONTRIBUTING.md). In every interaction and contribution, this project adheres to the [Contributor Covenant Code of Conduct](./docs/CODE_OF_CONDUCT.md).
+
+## Additional Resources
+
+- For monitoring upcoming changes and current proposals related to the technical implementation of the Polkadot network, visit the [`Requests for Comment (RFC)`](https://github.com/polkadot-fellows/RFCs) repository. While it's maintained by the Polkadot Fellowship, the RFC process welcomes contributions from everyone.
+

docs/CONTRIBUTING.md

@@ -96,9 +96,9 @@ d) that the docs team was included in the review process of a docs update
 
 We use [labels](https://github.com/paritytech/polkadot-sdk/labels) to manage PRs and issues and communicate
 state of a PR. Please familiarise yourself with them. Best way to get started is to a pick a ticket tagged
-`[easy](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AD0-easy)`
-or `[medium](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AD1-medium)`
-and get going or `[mentor](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AC1-mentor)`
+[easy](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AD0-easy)
+or [medium](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AD1-medium)
+and get going. Alternatively, look out for issues tagged [mentor](https://github.com/paritytech/polkadot-sdk/issues?q=is%3Aopen+is%3Aissue+label%3AC1-mentor)
 and get in contact with the mentor offering their support on that larger task.
 
 ****