Update docs on new model couplers

[infotroph]

Description

• Updated the text on coupling a new model, mostly by moving the Bety setup parts to the end and trying to capture all the lists that the package needs to be added to once it's merged and working.
• Added a model summary page for RothC
• random typo fixes

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.

[mdietze]

Just noticed that some comments I wrote days ago were never posted