[docs] More documentation rewriting.

docs/extension/docker.rst

@@ -1,8 +1,14 @@
-Docker Extension
-================
+Working with Docker
+===================
 
-.. todo:: The `bonobo-docker` package is at a very alpha stage, and things will change. This section is here to give a
-    brief overview but is neither complete nor definitive.
+.. include:: _beta.rst
 
 Read the introduction: https://www.bonobo-project.org/with/docker
 
+Source code
+:::::::::::
+
+https://github.com/python-bonobo/bonobo-docker
+
+
+