Added documentation on view specific hooks

This commit sponsored by Matthew Woodward.  Thank you!

docs/source/pluginwriter/api.rst

@@ -48,3 +48,65 @@ example might look like::
 This means that when people enable your plugin in their config you'll
 be able to provide defaults as well as type validation.
 
+
+Context Hooks
+-------------
+
+View specific hooks
++++++++++++++++++++
+
+You can hook up to almost any template called by any specific view
+fairly easily.  As long as the view directly or indirectly uses the
+method ``render_to_response`` you can access the context via a hook
+that has a key in the format of the tuple::
+
+  (view_symbolic_name, view_template_path)
+
+Where the "view symbolic name" is the same parameter used in
+``request.urlgen()`` to look up the test.  So say we're wanting to add
+something to the context of the user's homepage.  We look in
+mediagoblin/user_pages/routing.py and see::
+
+  add_route('mediagoblin.user_pages.user_home',
+            '/u/<string:user>/',
+            'mediagoblin.user_pages.views:user_home')
+
+Aha!  That means that the name is ``mediagoblin.user_pages.user_home``.
+Okay, so then we look at the view at the
+``mediagoblin.user_pages.views:user_home`` method::
+
+  @uses_pagination
+  def user_home(request, page):
+      # [...] whole bunch of stuff here
+      return render_to_response(
+          request,
+          'mediagoblin/user_pages/user.html',
+          {'user': user,
+           'user_gallery_url': user_gallery_url,
+           'media_entries': media_entries,
+           'pagination': pagination})
+
+Nice!  So the template appears to be
+``mediagoblin/user_pages/user.html``.  Cool, that means that the key
+is::
+
+  ("mediagoblin.user_pages.views:user_home",
+   "mediagoblin/user_pages/user.html")
+
+The context hook uses ``hook_transform()`` so that means that if we're
+hooking into it, our hook will both accept one argument, ``context``,
+and should return that modified object, like so::
+
+  def add_to_user_home_context(context):
+      context['foo'] = 'bar'
+      return context
+  
+  hooks = {
+      ("mediagoblin.user_pages.views:user_home",
+       "mediagoblin/user_pages/user.html"): add_to_user_home_context}
+
+
+Global context hook
++++++++++++++++++++
+
+