Update documentation about GroupHandler

README.mdown

@@ -47,6 +47,7 @@ Wrappers / Special Handlers
 - _FingersCrossedHandler_: A very interesting wrapper. It takes a logger as parameter and will accumulate log records of all levels until a record exceeds the defined severity level. At which point it delivers all records, including those of lower severity, to the handler it wraps. This means that until an error actually happens you will not see anything in your logs, but when it happens you will have the full information, including debug and info records. This provides you with all the information you need, but only when you need it.
 - _NullHandler_: Any record it can handle will be thrown away. This can be used to put on top of an existing handler stack to disable it temporarily.
 - _BufferHandler_: This handler will buffer all the log records it receives until close() is called at which point it will call handleBatch() on the handler it wraps with all the log messages at once. This is very useful to send an email with all records at once for example instead of having one mail for every log record.
+- _GroupHandler_: This handler groups other handlers. Every record received is sent to all the handlers it is configured with.
 - _TestHandler_: Used for testing, it records everything that is sent to it and has accessors to read out the information.
 
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