Start README.rst with a better title

Now that we are using gitea the contents of our README.rst are
more prominently displayed. Starting it with a "Team and repository
tags" title is a bit confusing. This change makes it start with the
name of the project instead.

Change-Id: Icc946b883e769aaaf2300477ab3e4d9af1e7dc74

README.rst

-========================
-Team and repository tags
-========================
+=============
+Kolla-Ansible
+=============
 
 .. image:: https://governance.openstack.org/tc/badges/kolla-ansible.svg
     :target: https://governance.openstack.org/tc/reference/tags/index.html
 
 .. Change things from this point on
 
-======================
-Kolla-Ansible Overview
-======================
 
 The Kolla-Ansible is a deliverable project separated from Kolla project.