Improved example of how to make FPGASim wrappers

This small MR improves documentation/example showing how to provide the wrapper file name argument. In addtion the default has some reasonable default.

Tagging @jahreda

Trigger/EFTracking/FPGATrackSim/FPGATrackSimConfTools/python/FPGATrackSimConfigFlags.py

@@ -4,7 +4,7 @@ def createFPGATrackSimConfigFlags():
     from AthenaConfiguration.AthConfigFlags import AthConfigFlags
     cf = AthConfigFlags()
     cf.addFlag('algoTag', 'Hough')
-    cf.addFlag('wrapperFileName', [])
+    cf.addFlag('wrapperFileName', "Wrapper.root")
 
     def __httHough1DFlags():
         """Additional function delays import"""