rearrange existing documentation to fit the new standard layout

Part of doc-migration work. For more detail, see:
https://specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration.html
https://etherpad.openstack.org/p/doc-migration-tracking

Change-Id: I545f16d6fe1fd3c2ed76f71b0ff79f93f3a1996e

doc/source/contributor/index.rst

@@ -1,4 +1,4 @@
 ============
 Contributing
 ============
-.. include:: ../../CONTRIBUTING.rst
+.. include:: ../../../CONTRIBUTING.rst

doc/source/index.rst

@@ -3,21 +3,22 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
-Welcome to ovsdbapp's documentation!
-========================================================
+.. the main title comes from README.rst
 
-Contents:
+.. include:: ../../README.rst
+
+Contents
+--------
 
 .. toctree::
    :maxdepth: 2
 
-   readme
-   installation
-   usage
-   contributing
+   install/index
+   user/index
+   contributor/index
 
 Indices and tables
-==================
+------------------
 
 * :ref:`genindex`
 * :ref:`modindex`

doc/source/readme.rst

@@ -1 +0,0 @@
-.. include:: ../../README.rst