Update documentation for adding a tracer and the tutorial

[apcraig]

PR checklist

• [X] Short (1 sentence) summary of your PR: Update documentation for adding a tracer and the tutorial
• [X] Developer(s): apcraig
• [X] Suggest PR reviewers from list in the column to the right.
• [X] Please copy the PR test results link or provide a summary of testing completed below. No testing done, just documentation changes
• 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
• [X] Please document the changes in detail, including why the changes are made. This will become part of the PR commit log.

Documentation is being update based on the Consortium workshop in 2024. The adding a tracer section has been updated as has the tutorial section related to adding a fluff tracer. An example set of code diffs for the tutorial is also includes as reference.

Closes #489

[apcraig]

Two sections of the documentation were modified, 5.5 (Adding tracers) and 6.2 (Icepack Tutorial). See the readthedocs link above and please suggest further changes.

[eclare108213]

@dabail10 please take a look at this when you have a chance. Thanks!