Add warning for FSD without waves, clarify documentation

[lettie-roach]

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PR checklist

• [x] Short (1 sentence) summary of your PR: Add warning for FSD without waves, clarify documentation
• [x] Developer(s): Lettie Roach
• [x] Suggest PR reviewers from list in the column to the right. @eclare108213 @apcraig
• [ ] Please copy the PR test results link or provide a summary of testing completed below. None
• How much do the PR code changes differ from the unmodified code?
  • [x] bit for bit
  • [ ] different at roundoff level
  • [ ] more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • [ ] Yes
  • [x] No
• Does this PR add any new test cases?
  • [ ] Yes
  • [x] 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/.)
  • [x] Yes
  • [ ] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [ ] No
• [ ] Please provide any additional information or relevant details below:

(@eclare108213 edited to to remove spaces from the checkboxes)

[apcraig]

This all looks pretty straight-forward, not sure where a new file comes in. I think this can be merged as is unless there are other things to do.

[lettie-roach]

Is there already a wave spectrum file for a whole year available? If so, then no extra file is needed. Cheyenne is down at the moment so I can't check what's in the ocn_data_dir

[apcraig]

The file we're using now for testing is ww3.20100101_efreq_remapgx3.nc. That file seems to have 6 hourly data for 1 day.

    time = UNLIMITED ; // (4 currently)
        time:units = "days since 1990-01-01 00:00:00" ;
 time = 7305, 7305.25, 7305.5, 7305.75 ;