Update accessbot instructions for OFTC

In order to accommodate the different permissions model on OFTC,
some changes were made to accessbot and its data structures. Correct
our documentation to reflect that.

Change-Id: I7a2c4201507dff2640b1506b885126d458b063a4

doc/source/irc.rst

@@ -243,8 +243,8 @@ Accessbot
 =========
 
 Accessbot defines access that should apply to all channels. Teams can add new
-channel to accessbot/channels.yaml and optionally keep channel operator
-permissions to the channel by specifying the full_mask option.
+channel to accessbot/channels.yaml and optionally set additional channel admins
+or ops, or specific mode overrides:
 
 Accessbot's configuration is in :config:`accessbot/channels.yaml`
 
@@ -252,8 +252,13 @@ Example:
 
 ::
 
-  - name: openstack-third-party-ci
-    mask: full_mask
+  - name: foo
+    mode: +bar
+    admins:
+    - baz
+    ops:
+    - xyzzy
+    - plugh
 
 PTG Bot
 =======