Cleanup README file
Cleanup README file

* remove deprecated tox environments
* remove deprecated Maven instructions
* cleanup syntax

Change-Id: I6b52a658ebd650f8a300a96d4bca200ba7ce687b

AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals