Fixes libtool bug https://bugs.gnu.org/42787.
The file lives in automake's git, not libtool.
* README.md: Change INSTALL URL to automake.git.
`Makefile`, `Makefile.in`, or `Makefile.am`. See the documentation for
details.
-[install]: http://git.savannah.gnu.org/cgit/libtool.git/tree/INSTALL
+[install]: http://git.savannah.gnu.org/cgit/automake.git/tree/INSTALL
[libtool]: http://www.gnu.org/s/libtool
[libtool list]: mailto:libtool@gnu.org
[news]: http://git.savannah.gnu.org/cgit/libtool.git/tree/NEWS