add documentation regarding removal of winston@2 support

Author: Matt Berther

README.md

@@ -6,6 +6,9 @@ A transport for [winston](https://github.com/winstonjs/winston) which logs to a
 
 Starting with version 2.0.0, the transport has been refactored to leverage the the [file-stream-rotator](https://github.com/rogerc/file-stream-rotator/) module. _Some of the options in the 1.x versions of the transport have changed._ Please review the options below to identify any changes needed.
 
+## Compatibility
+Please note that if you are using `winston@2`, you will need to use `winston-daily-rotate-file@3`. `winston-daily-rotate-file@4` removed support for `winston@2`.
+
 ## Install
 ```
 npm install winston-daily-rotate-file