sim: fix broken skel configure.ac example

Shell code before AC_INIT will be silently culled, and since the common
aclocal.m4 includes inline shell code, the file cannot be included before
AC_INIT.  So update the example to show people including the file after
that rather than before to avoid random breakage.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>