Update README.md

[karasowles]

What was changed

Changes

• Added link to the new temporal feature request board; while I was there, I also edited a few things:
  • updated how to contact the team since it's a larger group now and the name of the Slack channel has changed. If I'm incorrect here or you still want specific contacts feel free to revert
  • also added a link to the community page that allows folks to join the Slack

Why?

I'm adding feature request board links across our repos, and cleaning a few things. If I've misstepped for this particular repo, you're the experts, please feel free to re-work what I did

Checklist

1. Closes

2. How was this tested:

3. Any docs updates needed?

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[karasowles]

Update: I'm going through updating the repos to point to the new Feature Request Board at https://github.com/temporalio/temporal/discussions, but I just chatted to folks and it sounds like in the case of the TWC it might make sense for the feature requests to stay here instead