[MTE] Add comment about nested ScopedDisableMTE in test.

Change-Id: I02a4b44ebe1fad6f00b10d1083b43b52a0b5c316
diff --git a/tests/mte_test.cpp b/tests/mte_test.cpp
index ade9532..5eb804f 100644
--- a/tests/mte_test.cpp
+++ b/tests/mte_test.cpp
@@ -32,6 +32,7 @@
       reinterpret_cast<int*>(reinterpret_cast<uintptr_t>(p.get()) + (1ULL << 56));
   {
     ScopedDisableMTE x;
+    // Test that nested ScopedDisableMTE does not reset MTE state.
     { ScopedDisableMTE y; }
 #if defined(__aarch64__)
     volatile int load ATTRIBUTE_UNUSED = *mistagged_p;