test_case/DemoData

[cefect]

A few suggestions/questions on improving the test/demo data:

• It's unclear what the difference between the 'DemoData' and the 'test_case/PeeDee' folders are (it looks like a zip of the PeeDee case is actually duplicated inside 'DemoData'). It would be nice if this could be cleaned up.
• there is no documentation on the demo data. Where does it come from? What is each file? etc.
• outputs from the tool would also be helpful so the user can compare their outputs
• the PeeDee data appears to have invalid geometry (I created .\test_case\PeeDee\WaterExtent_fixed.gpkg with corrected geometry on my fork). Also, there are two tiny artifacts in the inundation polygon (see below) that cause problems for FwDET (even with the slope filtering). These should be fixed or mentioned in the readme so the user is not confused as to why their outputs are problematic.