Add CMS example

[Matthew Feickert]

@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?