Update README.md - good-graylog2 community plugin.
Update README.md - good-graylog2 community plugin.

We made a custom reporter for the log service graylog. Consider adding to your README.md. Thanks!
krambox/good,nkchouhan/good,netei/good,lancespeelmon/good,liatnjfrog/good,ldesplat/good,leore/good,eventhough/good,achingbrain/good