Explicitly stating that required validates boolean to be non default …

…zero value i.e. false

doc.go

@@ -253,7 +253,7 @@ Example #2
 
 This validates that the value is not the data types default zero value.
 For numbers ensures value is not zero. For strings ensures value is
-not "". For slices, maps, pointers, interfaces, channels and functions
+not "". For booleans ensures value is not false. For slices, maps, pointers, interfaces, channels and functions
 ensures the value is not nil. For structs ensures value is not the zero value when using WithRequiredStructEnabled.
 
  Usage: required