Document Hype subbasin should match

[sverhoeven]

The Hype model uses subbasins. The forcing and parameter set should use the same subbasins.

The documentation for the shape_file argument of ewatercycle.forcing.generate() should mention that the shape file should have the same subbasins as the subbasins used in the parameter set files like GeoData.txt.

Also to use Hype.get_value_at_coords(), the GeoData.txt needs to define latitude and longitude columns in GeoData.txt.