automake: info about Automake and Libtool being in different prefixes.

automake: info about Automake and Libtool being in different prefixes.

In response to https://bugs.gnu.org/71847.

* doc/automake.texi (Libtool library used but LIBTOOL is undefined):
new node. Tweak aclocal section.
* lib/Automake/Variable.pm (require_variables): refer to the
new node in the message for LT_INIT.
* maintainer/maint.mk (announcement) <AO>: new fn; use it
to output a link to the new node for test releases only.
* HACKING: mention M-x texinfo-master-menu, et al.
* doc/amhello/README: mention that the package is named amhello.