Added science guide documentation for sealvlponds

[davidclemenssewall]

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please refer to: https://github.com/CICE-Consortium/About-Us/wiki/Resource-Index#information-for-developers

PR checklist

• Short (1 sentence) summary of your PR:
  Added documentation of sealvlpond parameterization to the science guide.
• Developer(s):
  @davidclemenssewall
• Suggest PR reviewers from list in the column to the right.
  @dabail10
• Please copy the PR test results link or provide a summary of testing completed below.
  Tested documentation build on RTD (https://davidclemenssewall-icepack.readthedocs.io/en/sealvlponds_documentation/). No changes were made to code outside of the documentation.
• How much do the PR code changes differ from the unmodified code?
  • bit for bit
  • different at roundoff level
  • more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • Yes
  • No
• Does this PR add any new test cases?
  • Yes
  • No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.
  Added documentation of sealvlpond parameterization to the science guide.

[dabail10]

Looks good.