doc: Create directory structure for docs migration

The spec [1] recommends the following sections:

- install
- contributor
- configuration
- cli
- admin
- user
- reference

Only two of these are useful here:

- user
- reference

Add these and populate them.

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

Change-Id: Ieab6ad5ef43a172743053a1cffc8d46deb235277

doc/source/index.rst

@@ -2,16 +2,6 @@
 os-vif
 ======
 
-.. toctree::
-   :maxdepth: 2
-
-   vif_types
-   host_info
-   usage
-   plugins/ovs
-   plugins/linux-bridge
-   glossary
-
 `os-vif` is a library for plugging and unplugging virtual interfaces (VIFs) in
 OpenStack. It provides:
 
@@ -25,3 +15,23 @@ OpenStack. It provides:
 `os-vif` is intended to define a common model for representing VIF types in
 OpenStack. With the exception of the two included plugins, all plugins for
 other networking backends are maintained in separate code repositories.
+
+Usage Guide
+-----------
+
+.. toctree::
+   :maxdepth: 2
+
+   user/usage
+   user/vif-types
+   user/host-info
+   user/plugins/ovs
+   user/plugins/linux-bridge
+
+Reference
+---------
+
+.. toctree::
+   :maxdepth: 2
+
+   reference/glossary

doc/source/user/plugins/linux-bridge.rst

@@ -18,5 +18,5 @@ The Linux Bridge plugin provides support for the following VIF types:
 
   Refer to :ref:`vif-bridge` for more information.
 
-For information on the VIF type objects, refer to :doc:`../vif_types`. Note
+For information on the VIF type objects, refer to :doc:`/user/vif-types`. Note
 that only the above VIF types are supported by this plugin.

doc/source/user/plugins/ovs.rst

@@ -56,7 +56,7 @@ The Open vSwitch plugin provides support for the following VIF types:
 
   .. versionadded:: 1.5.0
 
-For information on the VIF type objects, refer to :doc:`../vif_types`. Note
+For information on the VIF type objects, refer to :doc:`/user/vif-types`. Note
 that only the above VIF types are supported by this plugin.
 
 __ http://docs.openvswitch.org/en/latest/howto/dpdk/