clarify documentation on how timer intervals should be specified

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@122240 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/timing.h

@@ -31,8 +31,8 @@
   The timing source used by Asterisk must provide the following
   features:
 
-  1) Periodic triggers, with a configurable interval (specified in
-     millisconds).
+  1) Periodic triggers, with a configurable interval (specified as
+     number of triggers per second).
 
   2) Multiple outstanding triggers, each of which must be 'acked'
      to clear it. Triggers must also be 'ackable' in quantity.