README update - rely on bug reporting doc and add section about community chat

Summary: Saw D11693 and I thought these changes on top might make the README even better? Open for discussion. I like our bug reporting doc a lot so I don't mind funneling users through it and not mentioning the bug reporting link directly in the readme. This notably forces github users to read a bit before they report issues to us for the first time. That said, I think the community chat can be really helpful at no cost to us so why not upsell it? This could fail if people start asking for say epriestley directly and / or the overall chatter is time consuming, but seemed worth tossing out at least.

Test Plan: read the text, asking opinions of cohorts

Reviewers: chad, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11694