Provide an issue template that helps separate live support from actual known+reproable project issues

[klardotsh]

This is IMO a failing of GitHub's UX, where "Issues" does not clearly mean "for end-users" or "for maintainers", but in general, we fall on the "for maintainers" end of the opinion spectrum here, and it's a bad first experience with the project to open an issue and immediately be told "well, thanks, but also, this is the wrong place, try Matrix/Discord".

Tangentially related is #437, as without somewhere that isn't an unending stream of text to sort through, we're missing an important mode of communication. I have more+new thoughts on that that I'll share on that issue next.

[grasegger]

@klardotsh As for issue templates have a look at this: https://github.com/mobxjs/mobx/issues/new/choose

One can set own links to zulip or github discussions.

I'd be happy to create a pr for templates and zulip links if you want.