Necessary improvements checklist

[mkavulich]

A few items did not make it in in time for the previous release, and there are some new documentation items that need updating:

• Details about available unit conversions per (Some available here, but needs updating: https://github.com/NCAR/ccpp-framework/blob/main/scripts/conversion_tools/unit_conversion.py)
• More detailed information about contributing code
• Add more details to scientific doc rules, especially on how to make block comments and examples of how they appear in the final documentation
  • Example: samfshalcnv.f --> https://dtcenter.ucar.edu/GMTB/UFS_SRW_App_v2.2.0/sci_doc/group___s_a_m_f__shal_ga7c9c5f5be5cf7b4f28738a89a9103939.html
• Add details on the required python environment for the CCPP framework