Documentation updates

[btobers]

No description provided.

[btobers]

Closes #102 system information requirements added to Installation documentation.

[btobers]

@drounce this is ready to review. Once this is pulled to the dev branch, I'll open PRs for PyGEM and PyGEM-notebooks to bring the main branches up to date with dev. Then we can release PyGEM v1.0.3 and Zenodo DOI tracking will go into effect.

Several updates rolled in here. Mainly this includes variable naming and documentation updates.

• The following variable names were updated:
  ref_gcm_name -> ref_climate_name
gcm_name -> sim_climate_name
scenario -> sim_climate_scenario
gcm_startyear -> sim_startyear
gcm_endyear -> sim_endyear
• Unused constants were removed from config.yaml
• Latex equation formatting issues were fixed in mass balance mode documentation
• Configuration file documentation was expanded upon and further clarified
• System info requirements added to install documentation
• PyGEM-notebooks test order enforced to avoid failured related to order notebooks are run in CLI testing workflow