Extensive documentation is available on the web at
<http://debathena.mit.edu/config-package-dev>.

Several ready-to-use examples are available in
/usr/share/doc/config-package-dev/examples

/usr/share/cdbs/1/rules/config-package.mk and the makefile fragments
that it includes also contain some basic documentation.  They are
fairly short, but may not be easy to ready without consulting the GNU
Make Manual (http://www.gnu.org/software/make/manual/make.html) and
inspecting the core CDBS rules files as well.
