Adding documentation for calibratable parameters

[peterlafollette]

In anticipation of the knowledge transfer, descriptions of calibratable parameters have been added.

Additions

-data/README.md has been added. It gives the list of calibratable parameters, including their name, units, physical limits, range included in stability testing, whether the parameter applies to individual soil layers or the whole model domain, and a description. General notes on parameters are then given, followed by example values from literature.

Removals

-

Changes

-The README in the main repo has been updated to give a clearer description of why the model should be applied in arid or semi-arid areas, as well as with a link to the calibratable parameters description. Note that this link will only work when the PR is merged to master, because the link is to the readme in the master branch, which will exist after the PR is approved.

Testing

1. No computational changes have been made, so no testing has occurred aside from the integrated tests.

Screenshots

Notes

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Todos

-

Checklist

• [x] PR has an informative and human-readable title
• [x] Changes are limited to a single goal (no scope creep)
• [x] Code can be automatically merged (no conflicts)
• [x] Code follows project standards (link if applicable)
• [x] Passes all existing automated tests
• [x] Any change in functionality is tested
• [x] New functions are documented (with a description, list of inputs, and expected output)
• [x] Placeholder code is flagged / future todos are captured in comments
• [x] Visually tested in supported browsers and devices (see checklist below :point_down:)
• [x] Project documentation has been updated (including the "Unreleased" section of the CHANGELOG)
• [x] Reviewers requested with the Reviewers tool :arrow_right:

Testing checklist

Target Environment support

• [ ] Windows
• [ ] Linux
• [ ] Browser

Accessibility

• [ ] Keyboard friendly
• [ ] Screen reader friendly

Other

• [ ] Is useable without CSS
• [ ] Is useable without JS
• [ ] Flexible from small to large screens
• [ ] No linting errors or warnings
• [ ] JavaScript tests are passing

[rlmcdaniel]

As discussed:

1. Typo in the range tested for stability for theta_r
2. Add where to set all calibratable parameters
3. Suggest adding units to the textural class table in addition to the description