[ussuri][goal] Update contributor documentation
[ussuri][goal] Update contributor documentation

This patch updates/adds the contributor documentation to follow
the guidelines of the Ussuri cycle community goal[1].

[1] https://governance.openstack.org/tc/goals/selected/ussuri/project-ptl-and-contrib-docs.html
Story: #2007236
Task: #38554

Change-Id: Ia0313f6fee6f7f4df7f1233e484dce583ada545d

openstack/openstack-ansible-openstack_hosts,openstack/openstack-ansible-openstack_hosts