Docs for developer scripts

[pearce8]

Update Benchpark script docs. The docs should describe the purpose of each script.

This PR adds documentation for 5 scripts, renames a script diffExperiments.py -> diffExperimentBuilds.py and adds a new script diffExperiments.py.

• Depends on Script to Compare Packages in Benchpark Against Spack Tag #648

• Purpose of 1 user script:

  • diffSpecs.py

• Purpose of 4 developer scripts:

  • diffExperiments.py
  • diffSystems.py
  • diffPackages.py
  • diffExperimentBuilds.py

• Directions on how to use the script.

• Provide an example including output.

• Do NOT include the code of the script, code is not a substitute for documentation.

[michaelmckinsey1]

Pros for making these scripts a command (benchpark diff):

• Easier to maintain (to integrate with pytest)
• Some scripts diffExperiments.py & diffSystems.py also diffExperimentBuilds.py share a lot of functionality.