Add anchor to template email

wiki/src/doc/about/openpgp_keys/signing_key_revocation.mdwn

@@ -250,6 +250,11 @@ At least every 2 years, we make sure that the mechanism still works:
 1. We write to the list to ask all members to check that they still have
    their share and the number in the file name.
 
+<a id="update"></a>
+
+Update email
+------------
+
 <pre>
 Subject: update