Adds openstack-doc IRC channel configuration for gerritbot.

(Not sure I have any pre-reqs for this patch but please review
to educate me.)

Patchset gets the channel name right.

Change-Id: I7d195253bacd2188e7c82ae69ef7e1690b8835be
Reviewed-on: https://review.openstack.org/21696
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Emilien Macchi <emilien@enovance.com>
Reviewed-by: Paul Belanger <paul.belanger@polybeacon.com>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins

modules/gerritbot/files/gerritbot_channel_config.yaml

@@ -50,6 +50,17 @@ openstack-dev:
     branches:
       - master
 
+openstack-doc:
+    events:
+      - patchset-created
+      - change-merged
+      - x-vrif-minus-2
+    projects:
+      - openstack/openstack-manuals
+      - openstack/api-site
+    branches:
+      - master
+
 stackforge-dev:
     events:
       - patchset-created