doc: suggest how to add suboptions

	  http://foosoftware.org/libfoo/

---------------------------

Of course, you can add other options to configure particular things in

your software. You can look at examples in other packages. The syntax

of the +Config.in+ file is the same as the one for the kernel Kconfig

file. The documentation for this syntax is available at

Of course, you can add other sub-options into a +if

BR2_PACKAGE_LIBFOO...endif+ statement to configure particular things

in your software. You can look at examples in other packages. The

syntax of the +Config.in+ file is the same as the one for the kernel

Kconfig file. The documentation for this syntax is available at

http://lxr.free-electrons.com/source/Documentation/kbuild/kconfig-language.txt[]

Finally you have to add your new +libfoo/Config.in+ to