Create CONTRIBUTING.md to capture how to contribute

[kidharb]

There are various ways to contribute to the project, ie sending a patch on email / discord or even through a pull request on Github.
This document should list the various ways to contribute and also list the preferred contribution method.
It should also mentions that contributions are very welcome

[rxrbln]

Contributing to T2 is super easy. Unlike many big name projects, we accept patches in any way shape or form. Just edit what you would like: fixing a typo, a bug, implementing a new package or features and run git diff or svn diff and send the resulting patch difference file to us via e-maill, GitHub issues, Discord, or other social media means. Preferable not mangling white-spaces, but even partially corrupted patches (from inline emails or web pasts) we usually try to fixup during review.

We will add this soon to a contributing file. What else should we list in it, help and guide newcomers?

[kidharb]

Are there tests that we can run on the patch before submitting?

[rxrbln]

given how long most builds take not really. - except of course we expect updates and new packages to be test built ;-)