Add some important notes to the documentation.
Add some important notes to the documentation.

joekiller/logstash-kafka,tinglinux/logstash-kafka,opentable/logstash-kafka,opentable/logstash-kafka,Aloomaio/logstash-kafka,joekiller/logstash-kafka,Aloomaio/logstash-kafka,tinglinux/logstash-kafka