* Add "Using Horizon" section to the docs, which describes
how to install and configure Horizon. It is for operators
who install Horizon from source code.
* Clean up README.rst as much of the information is out-of-date
and most of it is covered by the developer docs.
* Minor update of page titles.
Change-Id: I09aab0d0bc47e07c8d663e7f7b5801e456434950