Add a link to the relevant issue for ARM PAC handling

samples/sample_arm64.c

@@ -301,6 +301,9 @@ static void test_arm64_hook_mrs()
     }                       \
 } while(0)
 
+
+/* Test PAC support in the emulator. Code adapted from
+https://github.com/unicorn-engine/unicorn/issues/1789#issuecomment-1536320351 */
 static void test_arm64_pac(void)
 {
     uc_engine *uc;