Generate model output docs from model spec

[emlys]

Use the new output info in the model specs to generate much of the "interpreting results" section like we do for inputs.

[jagoldstein]

This should probably be a separate issue, but does it bother anyone else that "Interpreting Results" is nested beneath "Data Needs"? I advocate for moving all the "Interpreting Results" sections (from each model's chapter) up a level to be parallel with "Data Needs", rather than kept as a subheading.

[emlys]

@jagoldstein I agree! This is inconsistent between models and might just originate as a formatting mistake.