Add cautionary comment

Change-Id: I6003e8193bf58ba21cd8d5abe42959b489b2f39d

include/comphelper/profilezone.hxx

@@ -38,6 +38,10 @@ private:
     const char * m_sProfileId;
     long long m_aCreateTime;
 public:
+
+    // Note that the char pointer is stored as such in the ProfileZone object and used in the
+    // destructor, so be sure to pass a pointer that stays valid for the duration of the object's
+    // lifetime.
     ProfileZone(const char * sProfileId);
     ~ProfileZone();
 };