INSTALL: Add note that the GNU Autoconf Archive may be needed

As of 1a5417f (configure: Check linker for --image-base support),
the GNU Autoconf Archive is now required to bootstrap GRUB.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Author: crass

INSTALL

@@ -56,6 +56,7 @@ need the following.
 * Python 3 (NOTE: python 2.6 should still work, but it's not tested)
 * Autoconf 2.64 or later
 * Automake 1.14 or later
+* GNU Autoconf Archive (autoconf-archive on Debian)
 
 Your distro may package cross-compiling toolchains such as the following
 incomplete list on Debian: gcc-aarch64-linux-gnu, gcc-arm-linux-gnueabihf,