Merge pull request statsd#199 from Dieterbe/null_counter

document reset-to-0 behavior for counters

README.md

@@ -22,16 +22,19 @@ etc)
 general values should be integer.
 
 * *flush*
-  After the flush interval timeout (default 10 seconds), stats are
-  aggregated and sent to an upstream backend service.
+  After the flush interval timeout (defined by `config.flushInterval`,
+  default 10 seconds), stats are aggregated and sent to an upstream backend service.
 
 Counting
 --------
 
     gorets:1|c
 
-This is a simple counter. Add 1 to the "gorets" bucket. It stays in memory
-until the flush interval `config.flushInterval`.
+This is a simple counter. Add 1 to the "gorets" bucket.
+At each flush the current count is sent and reset to 0.
+If the count at flush is 0 then you can opt to send no metric at all for
+this counter, by setting `config.deleteCounters` (applies only to graphite
+backend).  Statsd will send both the rate as well as the count at each flush.
 
 ### Sampling