fanotify.7: Add some comments to example code

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

man7/fanotify.7

@@ -652,9 +652,10 @@ main(int argc, char *argv[])
     while (1) {
         poll_num = poll(fds, nfds, \-1);
         if (poll_num == \-1) {
-            if (errno == EINTR)
-                continue;
-            perror("poll");
+            if (errno == EINTR)     /* Interrupted by a signal */
+                continue;           /* Restart poll() */
+
+            perror("poll");         /* Unexpected error */
             exit(EXIT_FAILURE);
         }
         if (poll_num > 0) {