open.2: Mention O_PATH file descriptor use with fexecve(3)

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

man2/open.2

@@ -701,6 +701,11 @@ snprintf(buf, "/proc/self/fd/%d", fd);
 execl(buf, "some_prog", (char *) NULL);
 .EE
 .in
+.IP
+An
+.B O_PATH
+file descriptor can also be passed as the argument of
+.BR fexecve (3).
 .TP
 .B O_SYNC
 Write operations on the file will complete according to the requirements of