Update README.md

README.md

@@ -11,6 +11,7 @@ only takes four parameters, some of the required functions cannot be called sinc
 note: I choose NtShutdownSystem since its in every single windows version ever and inline hooking this function wouldnt cause any race conditions lol.
 
 ```cpp
+// taken from ReactOS: https://doxygen.reactos.org/dd/d1a/arm_2usercall_8c_source.html#l00082
 VOID KiSystemService(IN PKTHREAD Thread, IN PKTRAP_FRAME TrapFrame, IN ULONG Instruction)
 {
      // ... etc ....