Added example Nagios config, including command and service definitions.
Updated with mention of check_git.cfg.
Minor Markdown reformatting.
More Markdown updates.  Added notes about RedHat-style installation dir.
More Markdown fixes
Fixed a typo in step 4
Major changes:
* Try to automatically figure out where nagios utils.sh is located
* Use mktemp for REPO_DIR
* Added support for FreeBSD
* Allow repo arg to be placed anywhere in the command line
* Dynamically generate the GIT_SSH script, simplifying script installation

Minor changes, most in the effort to enable it to run on Linux or FreeBSD:
* Added a default PATH that should be enough for any commands used in the script.
* Took advantage of shell builtins like echo
* Derive script name using shell builtins instead of `echo|sed`
* Added some usage shortcuts: -h, -v, --key or -k
* Normalized whitespacing
Merge pull request #5 from oshaughnessy/master

Updated for FreeBSD support, other minor features and bug fixes