Docs: break apart the lengthy readme into organized docs

Also sphinx-ify where appropriate, and lots of general cleanup/editing.

docs/installation.rst

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+Installation
+============
+
+It's easiest to install Djrill from `PyPI <https://pypi.python.org/pypi/djrill>`_:
+
+    .. code-block:: console
+
+        $ pip install djrill
+
+If you decide to install Djrill some other way, you'll also need to install its
+one dependency (other than Django, of course): the `requests <http://docs.python-requests.org>`_
+library from Kenneth Reitz.
+
+
+Configuration
+-------------
+
+In your project's :file:`settings.py`:
+
+1. Add :mod:`djrill` to your :setting:`INSTALLED_APPS`::
+
+    INSTALLED_APPS = (
+        ...
+        "djrill"
+    )
+
+2. Add the following line, substituting your own :setting:`MANDRILL_API_KEY`::
+
+    MANDRILL_API_KEY = "brack3t-is-awesome"
+
+3. Override your existing :setting:`EMAIL_BACKEND` with the following line::
+
+    EMAIL_BACKEND = "djrill.mail.backends.djrill.DjrillBackend"
+
+
+Admin (Optional)
+----------------
+
+Djrill includes an optional Django admin interface, which allows you to:
+
+* Check the status of your Mandrill API connection
+* See stats on email senders, tags and urls
+
+If you want to enable the Djrill admin interface, edit your base :file:`urls.py`:
+
+    .. code-block:: python
+        :emphasize-lines: 4,6
+
+        ...
+        from django.contrib import admin
+
+        from djrill import DjrillAdminSite
+
+        admin.site = DjrillAdminSite()
+        admin.autodiscover()
+        ...
+
+        urlpatterns = patterns('',
+            ...
+            url(r'^admin/', include(admin.site.urls)),
+        )