Already we setup reno environment. So there were two Release notes
information: doc/source/releases and releasenotes (by reno).
Release Notes in doc directory are unnecessary.
It is not a good idea to have too much contents in the top page
document. Installation stuff is split into a separate page.
Title level of index.rst was inconsistent.
_static and _templates directories in releasenotes/source
are unnecessary. Also version info is set in release notes.
Change-Id: I0c2c31c9efc71d97ccea064da36302d886d8a743
45c763336f