Update upstart comments to reflect new commandline

```service puma start app=PATH_TO_APP`` is the correct syntax.
Uncomment setuid/setgid by default in upstart
Autodetect ruby managers and home directory in upstart script

- HOME is now picked up automatically from setuid.
- script will try rbenv, rvm, then chruby automatically.
- quoted heredoc to prevent /bin/sh interpreting variables early

Sponsored-by: CentroNet Marketing
Merge pull request #348 from CentroNet-Marketing/upstart-autodetect-ruby-managers

Upstart autodetect ruby managers