add a pager playbook for today's static mirror outage

Related to tpo/tpa/team#40432.

howto/static-component.md

@@ -169,11 +169,27 @@ If we do *not* want to keep a vanity site, we should also do this:
 
 ## Pager playbook
 
-TODO: add a pager playbook.
+### Out of date mirror
 
-<!-- information about common errors from the monitoring system and -->
-<!-- how to deal with them. this should be easy to follow: think of -->
-<!-- your future self, in a stressful situation, tired and hungry. -->
+If you see an error like this in Nagios:
+
+> mirror static sync - deb: CRITICAL: 1 mirror(s) not in sync (from oldest to newest): 95.216.163.36
+
+It means that Nagios has checked the given host
+(`hetzner-hel1-03.torproject.org`, in this case) is not in sync for
+the `deb` component, which is <https://deb.torproject.org>.
+
+In this case, it was because of a prolonged outage on that host, which
+made it unreachable to the master server ([tpo/tpa/team#40432](https://gitlab.torproject.org/tpo/tpa/team/-/issues/incident/40432)).
+
+The solution is to run a manual sync. This can be done by, for
+example, pushing to Jenkins or running `static-update-component` by
+hand, see [doc/static-sites](doc/static-sites).
+
+In this particular case, the solution is simply to run this on the
+static source (`palmeri` at the time of writing):
+
+    static-update-component deb.torproject.org
 
 ## Disaster recovery