Document paste deletion from the Lodgeit database

This is a straightforward administrative task, albeit not one we're
asked to perform often.

Change-Id: I582f70c76c2de1afd7a7c7f6319f3f0202fb7494

doc/source/paste.rst

@@ -33,3 +33,39 @@ anti-spam features required by OpenStack.
 
 Ansible configures lodgeit to use mariadb database backend, apache
 as a front-end proxy.
+
+Manual Administrative Tasks
+===========================
+
+Deleting a Paste
+----------------
+
+The quickest way to do this is database surgery. Lodgeit uses a
+MariaDB container on the paste server, and only has a single table
+in its database, so this is quite straightforward. Connect to the
+database with an interactive client session like so::
+
+  sudo docker-compose -f /etc/lodgeit-compose/docker-compose.yaml exec \
+    mariadb bash -c '/usr/bin/mysql -uroot -p"$MYSQL_ROOT_PASSWORD" lodgeit'
+
+These days we've configured Lodgeit to use so-called "private"
+identifiers by default, so that's what you'll likely be keying from.
+For the sake of example let's pretend the URL is
+``https://paste.opendev.org/show/thisIsSomeMadeUpBlob/``. First
+check the row you're about to delete::
+
+  SELECT code FROM pastes WHERE private_id='thisIsSomeMadeUpBlob';
+
+Note that if you instead have an old-style integer index identifier,
+you'll need to use ``paste_id`` with that instead of ``private_id``.
+You should see the ``code`` field content from one row matching the
+content of the page you're preparing to delete. If it looks correct,
+proceed with the deletion::
+
+  DELETE FROM pastes WHERE private_id='thisIsSomeMadeUpBlob';
+
+That command should return a response like ``1 row in set (0.001
+sec)`` if it was successful. Try to load the paste in your browser
+again and hopefully it now says ``PageNot Found`` instead of
+returning the prior content. If all's as intended, ``^D`` out of the
+interactive shell and you're done!