Document best practices for filing feature requests and other language repo interactions

It would be useful to have some short documents that we can point people to (and link in the README) about how to file effective feature requests (e.g. that problem statements are more useful than feature requests, at least in isolation). It also might be useful to provide some guidance to users on best practices for interacting with the issue tracker.

cc @natebosch

Start by reviewing the README and the existing issue tracker interactions to determine where links to guidance belong. Done means adding short documents covering effective feature requests and issue-tracker behavior, with the relevant guidance linked from the README.

Written by the indexing model from the issue text.