Adds a link to the [Polkadot SDK Version
Manager](https://github.com/paritytech/psvm) since this tool is not well
known, but very useful for developers using the Polkadot SDK.

---------

Co-authored-by: Bastian Köcher <[email protected]>

Minor edit to a broken link for Rust Docs on the README.md

Co-authored-by: Kian Paimani <[email protected]>

Was constantly failing, so here a fix.

This one also works and it is easier.

..and other high level docs.


# Polling 

Please vote in the reactions of this PR 

- 👍 I agree to replace the website of this repo to
https://paritytech.github.io/polkadot-sdk/master/polkadot_sdk_docs/index.html
- 👎 Keep it as polkadot.network
- 🤷

 Different opinion

---------

Co-authored-by: Bastian Köcher <[email protected]>

Co-authored-by: Liam Aharon <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>

Writing down the processes to do our releases.

Status: please review & approve so we can go ahead.

---------

Signed-off-by: Oliver Tale-Yazdi <[email protected]>
Co-authored-by: joe petrowski <[email protected]>
Co-authored-by: Liam Aharon <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: Jegor Sidorenko <[email protected]>

Co-authored-by: Liam Aharon <[email protected]>

This PR is a continuation of
https://github.com/paritytech/polkadot-sdk/pull/2102 and part of an
initiative started here https://hackmd.io/@romanp/rJ318ZCEp
What has been done:
- The content under `docs/*` (with the exception of `docs/mermaid`) has
been moved to `docs/contributor/`
- Developer Hub has been renamed to Polkadot SDK Docs, and the crate has
been renamed from `developer-hub` to `polkadot-sdk-docs`
- The content under `developer-hub/*` has been moved to `docs/sdk`

---
Original PR https://github.com/paritytech/polkadot-sdk/pull/2565, it has
been close due to too many rebase conflicts

---------

Co-authored-by: Serban Iorga <[email protected]>
Co-authored-by: Chevdor <[email protected]>
Co-authored-by: Egor_P <[email protected]>
Co-authored-by: Bastian Köcher <[email protected]>

* Add markdown linting

- add linter default rules
- adapt rules to current code
- fix the code for linting to pass
- add CI check

fix #1243

* Fix markdown for Substrate
* Fix tooling install
* Fix workflow
* Add documentation
* Remove trailing spaces
* Update .github/.markdownlint.yaml

Co-authored-by: Oliver Tale-Yazdi <[email protected]>
* Fix mangled markdown/lists
* Fix captalization issues on known words

* Added root README.md draft

* Modified Contribution section to reflect unified guidelines

* Update README.md

Co-authored-by: Squirrel <[email protected]>

* 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 <[email protected]>
Co-authored-by: Oliver Tale-Yazdi <[email protected]>