docs: add community documentation

This PR introduces:

1. Issue templates for bug reports and feature requests
1. Pull request template
1. Code of conduct, which reuses the content from angular/angular
1. Guidelines for contributing to the project
1. A development document which explains how to get started with fixing
issues/implementing new rules. There's more work here, this is just the
initial draft
1. Update of the readme to introduce project scope

Closes #334

PiperOrigin-RevId: 225438111