Tell maintainers to send urgent key updates to the list

For routine updates, we advise everyone to just upload the key to the
keyserver, but for anything urgent they should still send it to the
list.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

source/pgpkeys.rst

diff --git a/source/pgpkeys.rst b/source/pgpkeys.rst
index d036686..29726d7 100644
--- a/source/pgpkeys.rst
+++ b/source/pgpkeys.rst
@@ -113,4 +113,8 @@
     gpg -a --export your@email.addr > export.asc
 
 Then upload export.asc to https://keys.openpgp.org/upload/. We perform
-weekly updates to pgpkeys.git with the latest key data from keys.openpgp.org.
+periodic updates to pgpkeys.git with the latest key data from keys.openpgp.org.
+
+If the update is urgent, such as when you need to revoke a key or update
+the expiration date on a key that's about to expire, follow the
+"Submitting keys to the keyring" procedure described above.