Add documentation about upgrading Takahe (#486)

docs/index.rst

@@ -14,8 +14,9 @@ in alpha. For more information about Takahē, see
    :maxdepth: 2
    :caption: Contents:
 
-   installation
    features
+   installation
+   upgrading
    contributing
    domains
    moderation

docs/upgrading.rst

@@ -0,0 +1,22 @@
+Upgrading
+=========
+
+To upgrade Takahē you first need to pull the image by the tag name of the version
+you would like to upgrade to. Do this first before stopping your running container
+to reduce downtime waiting for the image to be downloaded.
+
+If you are using yaml based provisioning systems like docker compose or similar
+make sure you updated the pinned version like ``takahe:<version>`` (replacing
+``<version>`` by the desired version you are upgrading to).
+
+In case you are using tag name ``latest`` (e.g. ``takahe:latest``) just by pulling the
+image should be enough to fetch the latest.
+
+With the new image in your server you can now stop the running containers and spawn
+new ones that will pick the version you defined.
+
+.. warning::
+
+  If you are not running a startup container to perform data migrations before
+  starting the web server and the stator make sure you log into your container
+  to perform a data migration with ``python3 manage.py migrate``.