Add docs for restoring an etherpad

Signed-off-by: Dr. Jens Harbott <harbott@osism.tech>
Change-Id: I98c168145125cfa3a6f544b5751dfb936c8ae7ef

doc/source/etherpad.rst

@@ -14,14 +14,14 @@ At a Glance
 ===========
 
 :Hosts:
-  * http://etherpad.openstack.org
+  * https://etherpad.opendev.org
 :Ansible:
   * https://opendev.org/opendev/system-config
   * :git_file:`playbooks/roles/etherpad`
   * :git_file:`playbooks/service-etherpad.yaml`
   * :git_file:`inventory/service/host_vars/etherpad01.opendev.org.yaml`
 :Projects:
-  * http://etherpad.org/
+  * https://etherpad.org/
   * https://github.com/ether/etherpad-lite
 :Bugs:
   * https://storyboard.openstack.org/#!/project/748
@@ -65,3 +65,16 @@ welcome message boilerplate for a new pad. Check the pad's history and
 note that it has no authors and no prior revisions.
 
 .. _HTTP API: https://github.com/ether/etherpad-lite/wiki/HTTP-API
+
+Restoring a Pad
+---------------
+
+It also happens that the content of a pad gets overwritten with the
+wrong content, one common example is someone using a translation tool
+on it, not being aware that this changes the document for everyone
+instead of just locally. Via the revision slider you can identify the
+last good version and then restore it via the API::
+
+  wget -qO- "http://localhost:9001/api/1.2.11/restoreRevision?apikey=$(sudo \
+  docker-compose -f /etc/etherpad-docker/docker-compose.yaml exec etherpad \
+  cat /opt/etherpad-lite/APIKEY.txt)&padID=XXXXXXXXXX&rev=NNN" ; echo