update comment for subgroup attack

readme.md

@@ -280,9 +280,9 @@ getStr() method gets
 * `3 <x>` ; compressed format for odd y
 
 ## Verify an element in G2
-`G2::isValid()` checks that the element is in the curve of G2 and the order of it is r.
+`G2::isValid()` checks that the element is in the curve of G2 and the order of it is r for subgroup attack.
 `G2::set()`, `G2::setStr` and `operator<<` also check the order.
-If you check it out of the library, then you can stop the verification by calling `G2::setOrder(0)`.
+If you check it out of the library, then you can stop the verification by calling `G2::verifyOrderG2(false)`.
 
 # How to make asm files (optional)
 The asm files generated by this way are already put in `src/asm`, then it is not necessary to do this.