Use a more specific name

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

@@ -104,8 +104,8 @@ There is no expiry date on revocation certificates. One way of
 cancelling the revocation power is to destroy all copies of shares of 2
 groups amongst B, C, or D.
 
-Email to members of the groups
-==============================
+Invitation email
+================
 
 <pre>
 Subject: distribution