doc migration: new directory layout

This patch introduces a new directory layout
in doc/source in conformance with the OpenStack
manuals project migration spec [1], moves the
existing content in manila/doc/source into the
new directories, and adjusts index files accordingly.

This is the first step in the migration process
as outlined in the spec.

[1] https://specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration.html

Partial-Bug: #1706181
Change-Id: I6b876f6e697659a5fe7046d5c5d4fd4ed98f9828
Needed-By: If13ebd1ede6fbc997d74425ec78e15621f1f80b2
Depends-On: I834fbef9783739fd664246ff710df1ab42ce2af5
Depends-On: Ia750cb049c0f53a234ea70ce1f2bbbb7a2aa9454

doc/source/contributor/contributing.rst

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

doc/source/contributor/readme.rst

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

doc/source/index.rst

@@ -4,15 +4,15 @@
    contain the root `toctree` directive.
 
 Welcome to manila-image-elements documentation!
-========================================================
+===============================================
 
 Contents:
 
 .. toctree::
    :maxdepth: 2
 
-   readme
-   contributing
+   contributor/readme
+   contributor/contributing
 
 Indices and tables
 ==================

doc/source/readme.rst

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