Lots of documentation changes

* added a YouCanHelp directive to replace FIXMEs and encourage contributors
  to help out
* moved some bits around between the hacking howto and the codebase documents
* expanded on the stub nature of the theming howto
* tweaked some other text

docs/codebase.rst

@@ -7,6 +7,18 @@
 This chapter covers the libraries that GNU MediaGoblin uses as well as
 various recipes for getting things done.
 
+.. Note::
+
+   This chapter is in flux.  Clearly there are things here that aren't
+   documented.  If there's something you have questions about, please
+   ask!
+
+   See `the join page on the website <http://mediagoblin.org/join/>`_
+   for where we hang out.
+
+For more information on how to get started hacking on GNU MediaGoblin,
+see :ref:`hacking-howto`.
+
 
 Software Stack
 ==============
@@ -59,6 +71,55 @@ Software Stack
   * `JQuery <http://jquery.com/>`_: for groovy JavaScript things
 
 
+
+What's where
+============
+
+After you've run buildout, you're faced with the following directory
+tree::
+
+    mediagoblin/
+    |- mediagoblin/              source code
+    |  |- tests/
+    |  |- templates/
+    |  |- auth/
+    |  \- submit/
+    |- docs/                     documentation
+    |
+    |        the rest of these directories are generated by
+    |        buildout.
+    |
+    |- bin/                      scripts
+    |- develop-eggs/
+    |- eggs/
+    |- mediagoblin.egg-info/
+    |- parts/
+    |- user_dev/                 sessions, etc
+
+
+As you can see, all the code for GNU MediaGoblin is in the
+``mediagoblin`` directory.
+
+Here are some interesting files and what they do:
+
+:routing.py: maps url paths to views
+:views.py:   views handle http requests
+:models.py:  holds the mongodb schemas---these are the data structures 
+             we're working with
+
+You'll notice that there are several sub-directories: tests,
+templates, auth, submit, ...
+
+``tests`` holds the unit test code.
+
+``templates`` holds all the templates for the output.
+
+``auth`` and ``submit`` are modules that enacpsulate authentication
+and media item submission.  If you look in these directories, you'll
+see they have their own ``routing.py``, ``view.py``, and
+``models.py`` in addition to some other code.
+
+
 Recipes
 =======