clarify CICE citation info in doc

[eclare108213]

• Short (1 sentence) summary of your PR:
  Modifying information in the documentation about how to cite the code (see CICE issue model citation guidance #465)
• Developer(s):
  E. Hunke
• Suggest PR reviewers from list in the column to the right.
• Please copy the PR test results link or provide a summary of testing completed below.
  No changes to the code base, only 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 Icepack 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/. A test build of the technical docs will be performed as part of the PR testing.)
  • Yes
  • No, does the documentation need to be updated at a later time?
    • Yes
    • No
• Please provide any additional information or relevant details below:
  Except for the code names and version numbers/DOIs, this is identical to the text for Icepack in PR#327