Add CMS example

[matthewfeickert]

@kpedro88 @nsmith- Can I get you to give me an example of how CMS uses CVMFS to setup environments similar to

cvmfs-venv/README.md

Lines 61 to 66 in 41f05ce

	* Create a Python 3 virtual environment named 'alrb-example' with the Python
	runtime provided by ATLAS AnalysisBase release v22.2.113.
	setupATLAS -3
	asetup AnalysisBase,22.2.113
	. cvmfs-venv alrb-example

so that I could add an example to the --help option?