Have chat links better integrated into the student guideline

[bsipocz]

It would be useful to have a better visibility to the given suborgs (and their varying application process and chat channels) in the student application guideline page.
Alternatively, those links could be repeated in every project idea page.

Looking at that guide with fresh eyes, it's not trivial to see of how to e.g. access the heliopy chat/developers, so students end up in the astropy sign up mailing list. I assume it also works the other way and astropy interests end up elsewhere.

[dpshelio]

A "show interest" button for each idea where links to either astropy's form/slack, matrix channels or mailing lists depending of the sub-org will be great.

[RajasBharambe]

Hey there, I wanted to contribute and resolve the issue !