Add a support file to repository to help new contributors

[annezazu]

Is your feature request related to a problem? Please describe.

In looking through GitHub's docs, I found this option: https://docs.github.com/en/free-pro-team@latest/github/building-a-strong-community/adding-support-resources-to-your-project

Essentially, you can add a support file to help people get familiar with the repository when new. This seems like a high impact, low effort way to perhaps help with engagement and help guide people towards our best practices.

Describe the solution you'd like

I'd love to see a support file created that includes links to these two references:

https://github.com/WordPress/gutenberg/blob/master/CONTRIBUTING.md
https://github.com/WordPress/gutenberg/blob/master/CODE_OF_CONDUCT.md

fyi to @mkaz :) I'll try to get to this in the future but wanted to open the issue for now.

[skorasaurus]

done in #27524 :)