Minor/useful tweaks to Sahara repo descriptions
Minor/useful tweaks to Sahara repo descriptions

plugins->plugin (each repo contains just one plugin)

Improve grammar/diction in Sahara description (borrowed from version
found in governance repo)

Change-Id: I5c291bed0be444688fe4a99e3be83e6a0e444fa2

openstack-infra/project-config,openstack-infra/project-config