Doc needs inputs to DATA_ASSIMILATION_SCRIPT

In the workflow documentation for 'Data assimilation controls' (#3 in https://esmci.github.io/cime/users_guide/workflows.html?highlight=cycles), the description for `DATA_ASSIMILATION_SCRIPT` describes a script but not the inputs to that script.

The script is passed four arguments.

1. The case root directory
2. The cycle number (zero based)
3. The `lid` for the just-completed run
4. The case run directory

Also, since `DATA_ASSIMILATION_SCRIPT` and `DATA_ASSIMILATION_CYCLES` can be use for any purpose, I suggest renaming that section or just explaining that those two keywords and be used with any script and as long as no `DATA_ASSIMILATION_XXX` XML variables are set (for `XXX` = a model component type), no data assimilation is done.