By default, when a Solr contributor creates their own fork, only they
have access to that fork. This creates a bit of a roadblock when users
contribute PRs from these forks - others can't build off of their work -
something that is done often with patches. An initial user might
contribute a feature, a committer might add tests or change formatting,
etc.
This commit introduces a bullet point to our PR checklist to nudge users
towards making their PR branches more open so that it's easier for committers
to help them.