Add composer suggest for Rollbar package.

Update documentation.

README.mdown

@@ -133,6 +133,7 @@ Handlers
 - _ZendMonitorHandler_: Logs records to the Zend Monitor present in Zend Server.
 - _NewRelicHandler_: Logs records to a [NewRelic](http://newrelic.com/) application.
 - _LogglyHandler_: Logs records to a [Loggly](http://www.loggly.com/) account.
+- _RollbarHandler_: Logs records to a [Rollbar](https://rollbar.com/) account.
 - _SyslogUdpHandler_: Logs records to a remote [Syslogd](http://www.rsyslog.com/) server.
 
 ### Logging in development

composer.json

@@ -31,7 +31,8 @@
         "ruflin/elastica": "Allow sending log messages to an Elastic Search server",
         "ext-amqp": "Allow sending log messages to an AMQP server (1.0+ required)",
         "ext-mongo": "Allow sending log messages to a MongoDB server",
-        "aws/aws-sdk-php": "Allow sending log messages to AWS services like DynamoDB"
+        "aws/aws-sdk-php": "Allow sending log messages to AWS services like DynamoDB",
+        "rollbar/rollbar": "Allow sending log messages to Rollbar"
     },
     "autoload": {
         "psr-4": {"Monolog\\": "src/Monolog"}