make README more friendly for first-time users

[binary1230]

specifically one thing I just lost an afternoon to, I had never setup logstash before and the README example includes this line:

 'cpuprofile       => '/path/to/write/cpu/profile/to/file','

including this line causes a CPU profile to be written and then logstash-forwarder to exit in 60 seconds what looks like a crash (but isn't).

it would be worth moving this option to some kind of "advanced options" section of the README with a BIG NOTE that says not to enable it for production environments.