Modified site.pp.example to enable feature

Nagios check for ceph
Minor language correction, style fix

This commit fixes some grammar errors in a comment and
corrects a puppet-lint issue by using single quotes around
a class name.

Partial-Blueprint: nagios-check-for-ceph
Merge pull request #1 from markvoelker/ceph-nagios-check

Minor language correction, style fix
Merge pull request #194 from satroutr/ceph-nagios-check

Modified site.pp.example to enable feature