Prepare guidance for model selection, configuration, assessment, & troubleshooting

> CDI Proposal Tier 3: Prepare more extensive guidance to help users select a suitable model configuration for their site, assess model results, and troubleshoot surprising outputs.

No files, tests, or entry points are named. Start by locating the existing guidance for model selection, configuration, result assessment, and troubleshooting, then identify the gaps this issue should cover. Done means users can choose a suitable configuration, assess model results, and troubleshoot surprising outputs using the resulting guidance.

Written by the indexing model from the issue text.