Update message for model error when soil profile reaches the maximum number of soil layers

[fabiooliveira72]

The maximum number of soil layers in DSSAT is 20. However, the MODEL.ERR message that shows up is somewhat confusing. For example, if you have defined 21 layers in the soil profile the model will stop and show this message:

More than 19 layers in the soil profile. Correct input file.
File: IU.SOL Line: 36 Error key: IPSOIL

Additional information may be available in WARNING.OUT file.

There is a need to update this message