User's Guide: Force h2i in GDD-Generating workflow

[samsrabin]

(Step 4 in parent issue #3319. Only necessary if Step 1, #3320, indicates this is a good idea.)

What sort(s) of documentation issue is this?

• Something is missing.
• Something is (or might be) incorrect or outdated.
• Something is confusing.
• Something is broken.

What part(s) of the documentation does this concern?

• Technical Note (science and design of the model)
• User's Guide (using the model and related tools)
• Somewhere else (e.g., README file, tool help text, or code comment): Please specify
• I don't know

Describe the issue

I think it would be better to request instantaneous GDDACCUM and GDDHARV in the GDD-generating workflow. See #3319 for more details.

See #3332 for additional updates that could happen when addressing this.

[samsrabin]

Blocked by #3445.