Add info about updating repos

Repos should have:

- add the `help wanted` label
- add an issue to make `main` the primary branch (instead of `master`) if it is not already done. This is for consistency, since new GitHub packages work this way and many folks have already started migrating existing repos. Making the repos in this org consistent will help maintainers.
- make sure the settings are consistent; merged branches should be automatically deleted (this is in settings)