Switch between OpenStack versions docs update.

After implementing possibility to switch between OpenStack
version flexibly using the origins configuration files -
the following sections were updated in the documentation:
* 'Configurations' section on the features page:
  - origins files location
* 'Configuration' section on the getting started page:
  - how to include origins file in command line
* 'How do I run a specific OpenStack milestone' section
  on the 'Questions and Answers' page:
  - origins configuration file parameters
  - specifying component branch/tag

Change-Id: I6ad2288b3f919531af02b553ed86d16536fc75e1

docs/source/topics/features.rst

@@ -8,12 +8,13 @@ Features
 Configurations
 --------------
 
-A set of configuration files (in yaml format) that shows common/component/distribution configurations.
+A set of configuration files (in yaml format) that shows common/component/distribution/origins configurations.
 All the yaml configuration files could be found in:
 
 * conf/templates/keystone/
 * conf/components/
 * conf/distros/
+* conf/origins/
 * subdirectories of conf/personas/
 
 

docs/source/topics/gettingstarted.rst

@@ -152,6 +152,9 @@ to fit your desired configuration of nova/glance and the other OpenStack compone
 You can use ``-p <conf/components/required_file.yaml>`` option with following commands
 to use configuration files.
 
+To specify which versions of OpenStack components you want to install select or edit origins configuration
+file from ``<conf/origins/>`` and use it as follows ``-o <conf/origins/origins_file.yaml>``.
+
 Networking notes for those on RedHat/CentOS/Fedora
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/source/topics/qanda.rst

@@ -38,23 +38,24 @@ run against a specific milestone of OpenStack just checkout the
 same tag in anvil and run the same actions as
 you would have ran previously. 
 
-An example of this, lets adjust nova to use the ``stable/essex`` branch.
+An example of this, lets adjust ``nova`` to use the ``stable/essex`` branch.
 
-- Open ``conf/components/nova.yaml`` in your favorite editor
-- Locate the line that starts with ``get_from:`` and either change
-  it to a new github location
+- Open ``conf/origins/master.yaml`` file in your favorite editor
+- Locate lines that describe the ``nova`` component
+- Change branch parameter to the desired one
 
 ::
 
-    # Where we download this from...
-    get_from: "git://github.com/openstack/nova.git?branch=stable/essex"
+    nova:
+        repo: git://github.com/openstack/nova.git
+        branch: stable/essex
 
+- Component origin parameters are:
+  - ``repo: <repo_url>`` - required
+  - ``branch: <branch>`` - optional
+  - ``tag: <tag>`` - optional
+  If no branch nor tag parameters were specified then ``branch: master`` is used by default.
 
-- The special keywords here are ``branch=``
-  and ``tag=`` which are ways for anvil to parse out which branch/tag
-  you desire. 
-
-  - **Note:** this is not git official syntax
   - **Note:** tag overrides branch (so you can't really include both)