Update GelfAmqpAppender.cs

As a publisher of log, you expect the log server to take care of the creation of the exchange and queues : that what graylog2 do with rabbit mq. BasicPublish work with exchange and key not queue.
Update README.md

Publish log to exchange and key not to queue.
Merge pull request #11 from plemanach/master

Graylog2 server amqp(Rabbit mq).