Add MOM6 instructions to Horizontal_Regridding.ipynb

[adele-morrison]

Add documentation at top of recipe with MOM6 variable names and any grid/diagnostic differences that users need to be aware of if they want to convert the recipe on their own to use MOM6 output.

Add explanatory comment on what lon_b/lat_b are.

Also remove cf-xarray/pint.

And rename Horizontal_Regridding_Compare_Resolutions.ipynb?