Guidelines for contributors (staff but also users)

This document is added to the source to outline expectations for staff and users contributing to the docs project.

@rjhartmanbaker and @brandon_cook have kindly agreed to serve as contacts.

@rjhartmanbaker further has discussed scope of the policy vs the LBL RPM, and a statement at the top includes a link to the relevant LBL RPM policy.

This is based on the Contributor Covenant v2.0: https://www.contributor-covenant.org/