Add channel-specific options example for accessbot

Show how to go about adding admins or ops to a channel, as well as
doing channel-specific mode overrides.

Change-Id: I591c5467c94598c220292693bcb674e4f9d23c28

accessbot/channels.yaml

@@ -33,8 +33,19 @@
 #
 # NOTE each channel looks up these values in the "global:" list first.
 # Channel specific values override the global values.
-
 #
+# For example...
+#
+# channels:
+#   - name: foochannel
+#     admins:
+#     - xyzzy
+#     - plugh
+#     ops:
+#     - gralpy
+#   - name: barchannel
+#     mode: +baz
+
 # Global definitions
 #