timer_create.2: Strengthen the warning about use of printf() in the example program

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/timer_create.2

@@ -381,9 +381,11 @@ print_siginfo(siginfo_t *si)
 static void
 handler(int sig, siginfo_t *si, void *uc)
 {
-    /* Note: calling printf() from a signal handler is not
-       strictly correct, since printf() is not async\-signal\-safe;
-       see signal-safety(7) */
+    /* Note: calling printf() from a signal handler is not safe
+       (and should not be done in production programs), since
+       printf() is not async\-signal\-safe; see signal-safety(7).
+       Nevertheless, we use printf() here as a simple way of
+       showing that the handler was called. */
 
     printf("Caught signal %d\\n", sig);
     print_siginfo(si);