Document the meaning and units of measurement of all the parameters.

[axch]

For now, expanding the comments in the top-level parameters.in file is an adequate place to capture this knowledge. I believe Fortran namelist input permits interspersing line comments with the entries of the namelist, and may even permit comments at the end of a line, like

 &NUMERICS
 au = 200.,  ! viscosity, in Pa * s
 ah = 0.0,   ! thickness diffusivity, in m^2/s
 ...

[edoddridge]

This was closed by #135, which added a new config file to the base directory of the repo that included comments describing each of the parameters, and displayed this file in the documentation.

[axch]

Just a couple little nits from looking that file over:

• What are the units in which the Coriolis parameter is given?
• Can you give the bit meanings for the wetmask (1 for water and 0 for land?)