README.md in fluent-plugin-cloudwatch-1.2.11 vs README.md in fluent-plugin-cloudwatch-1.2.12

- old
+ new

@@ -210,9 +210,19 @@
 
 ## config: delayed_start
 
 When config `delayed_start` is set true, plugin startup will be delayed in random seconds(0 ~ interval).
 
+## config: offset
+
+unit: seconds.
+
+flunet-plugin-cloudwatch gets metrics between now and `period` &times; 10 sec ago, and pick a latest value from that.
+
+But the latest metric is insufficient for `statistics Sum`.
+
+If `offset` is specified, fluent-plugin-cloudwatch gets metrics between `offset` sec ago and older.
+
 ## Contributing
 
 1. Fork it
 2. Create your feature branch (`git checkout -b my-new-feature`)
 3. Commit your changes (`git commit -am 'Added some feature'`)