docs: Add menu to prevent older makeinfo versions from failing

docs: Add menu to prevent older makeinfo versions from failing

It has been reported that makeinfo version 4.13a complains and returns
error when menus for chapter structuring commands are not present. It
is also known that newer makeinfos, such as version 6.7, will create
default menus when needed. Since the menu will be created regardless,
explicitly create it to support older makeinfo versions. This also
enables building to be successful when an older makeinfo is installed
because in that case info files are attempted to be generated with the
"all" target.

Reported-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-by: Olaf Hering <olaf@aepfle.de>