Update hidpp20.py

We probably should add a comment here so this makes sense later on. Otherwise, this looks good.

lib/logitech_receiver/hidpp20.py

@@ -301,6 +301,7 @@ class FeaturesArray(dict):
         feature = self.inverse.get(index)
         if feature is not None:
             return feature
+        # Sub-device index; bridge unwrap offsets by 0x100 (see listener). 
         if index >= 0x100:
             return self.sub_inverse.get(index - 0x100)
         elif self._check():