Add an explanation to release tag merges
Add an explanation to release tag merges

Merge commits look strange in Gerrit to begin with, and the
reasoning behind release tag merges is unknown to many of our
community, even core reviewers of prominent projects. Better commit
messages, along with evangelization from release management and
infra, should go a long way toward making sure they're approved in a
timely fashion.

Change-Id: I4521e37ee276b6182dd29cc02fba78861ea8d95e

openstack-infra/project-config,noorul/os-project-config,coolsvap/project-config,anbangr/osci-project-config,openstack-infra/project-config,dongwenjuan/project-config,dongwenjuan/project-config,coolsvap/project-config,noorul/os-project-config,anbangr/osci-project-config,Tesora/tesora-project-config,Tesora/tesora-project-config