Link the contributing guidelines in CONTRIBUTING.md

[apiraino]

This file is supposed to be the entrypoint for new contributors, so it's helpful if we point them also to our extensive documentation about how to start interacting with the project.

The rest of the document will help with the more technical aspects (and where to ask for help).

Discussed on Zulip.

cc @jyn514

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[jyn514]

This file is supposed to be the entrypoint for new contributors, so it's helpful if we point them also to our extensive documentation about how to start interacting with the project.

according to who? my impression has always been that https://rustc-dev-guide.rust-lang.org/ is the entrypoint for new contributors; i didn't even know this forge link existed. i note that there's a bunch of docs duplicated between the two.

i also want to note that this is the very first link at the very top of CONTRIBUTING.md, which means that it's going to be the first thing people click. i would really prefer to keep zulip as the first link and only add the reference documentation below it.

[Kobzol]

We periodically get new people coming to Zulip, who say something about them and say hi, and then maybe get an emoji response back.

Going to Zulip can be a useful pathway, but we should also have some actual written documentation that tells people some ground rules and how to begin. We have such a page, and so IMO we should link to it in the contributing file (an alternative would be to write all that down in CONTRIBUTING.md, but I think it is more practical to keep that info in the Forge, at least for now).