Update Docker README

This patch updates the docker README file to include the --link arg
to the command for launching a Mistral container to ensure the
rabbitmq and mistral containers can communicate.

This patch also adds a new section that explains how and why to
mount the Mistral source code as a volume in a running container.

Change-Id: Iec25f7e7dfda0bc8c9b38fa37b048448d73f66e4
Co-Authored-By: Brad Crochet <brad@redhat.com>

tools/docker/DOCKER_README.rst

@@ -20,7 +20,6 @@ on this process, check out `the official guide at
 <http://www.sqlite.org/omitted.html>`_.
 
 
-
 Build the Mistral image
 -----------------------
 
@@ -36,7 +35,7 @@ Start a RabbitMQ container::
 
 Start Mistral::
 
-  docker run -d -p 8989:8989 --name mistral mistral-all
+  docker run -d  --link rabbitmq:rabbitmq -p 8989:8989 --name mistral mistral-all
 
 To execute commands inside the container::
 
@@ -47,11 +46,40 @@ E.g. to list workflows, issue::
   mistral workflow-list
 
 
+Running Mistral From A Volume
+-----------------------------
+
+A scenario you may find useful for development is to clone a Mistral git repo
+and link it into the container via a volume. This will allow you to make changes
+to the Mistral source on your local machine and execute them immediately in the
+container.
+
+The following example illustrates launching the container from the local
+directory of a git repo clone of Mistral.::
+
+  docker run -d --link rabbitmq:rabbitmq -v $(pwd):/opt/stack/mistral:Z -p 8989:8989 --name mistral mistral-all
+
+You might want to mount an additional drive to move files easily between your
+development computer and the container.  An easy way to do this is to mount an
+additional volume that maps to /home/mistral/ in the container.
+
+Since the directory is already being used to store the mistral.conf and
+mistral.sqlite files, you will want to copy these to the local directory you
+intend to use for the mount. This example assumes the directory to mount is
+"/tmp/mistral".  You should change this to the actual directory you intend to
+use.::
+
+  docker cp mistral:/home/mistral/mistral.conf /tmp/mistral/mistral.conf
+  docker cp mistral:/home/mistral/mistral.sqlite /tmp/mistral/mistral.sqlite
+
+  docker run -d --link rabbitmq:rabbitmq -v $(pwd):/opt/stack/mistral:Z -v /tmp/mistral:/home/mistral:Z -p 8989:8989 --name mistral mistral-all
+
+
 Running Mistral with MySQL
 --------------------------
 
 Other than the simplest use cases will very probably fail with various errors
-due to the default Sqlight database. It is highly recommended that, for
+due to the default Sqlite database. It is highly recommended that, for
 example, MySQL is used as database backend.
 
 The `start_mistral_rabbit_mysql.sh` script sets up a rabbitmq container, a