logstash cookbook update

added 'limit nofile 65550 65550' to upstart recipe as I learned the hard way upstart doesn't respect ulimits.

added cookbook page on running logstash on existing centralized rsyslog server ..  mostly copy and paste from other examples, but I figure there's a bunch of people that would already have a central syslog server and want to use it  as an aggregation point for logstash.

not totally sure the markdown is correct as jekyll kept complaining about the 'include_code' tags and I'm too tired to learn something new tonight.   If the formatting is bad  point angrily at me and I'll try and fix tomorrow.

![110607-family-guy-evil-monkey](https://f.cloud.github.com/assets/2488346/99498/9d815a50-6772-11e2-82c6-a9b0be942a43.jpg)