Document new processes in contributing docs

[tim-schilling]

As per our November 2024 meeting, we are now identifying top priorities for the library. This helps people see what issues are important to the library and should help encourage contributors who want to make a larger impact.

We need to document the following:

• What the top priority label means and how to use it
• The contributor discussion meetings (maybe just say they happen?)
• How to use discussions
• Adding resources of using the toolbar or contributing to the toolbar to the Show & Tell area of discussions