Docs update model install instructions

[man080107]

Description

Motivation and Context

Review Time Estimate

• Immediately
• Within one week
• When possible

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• My name is in the list of CITATION.cff
• I agree that PEcAn Project may distribute my contribution under any or all of
  • the same license as the existing code,
  • and/or the BSD 3-clause license.
• I have updated the CHANGELOG.md.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

#Fixes #3741

[infotroph]

Apparently I started reviewing this some time ago and never posted my comments. I think this is a solid improvement that needs a bit more iteration -- see my inline comments for details.

[man080107]

Thank you for the thoughtful review and the inline comments. I’m glad to hear this is a solid improvement. I’ll address the suggested changes and push an updated version shortly..