To help with man-db development, you'll probably want to start by
checking out the latest code from revision control. Use the
bzr client to check out
http://bzr.savannah.nongnu.org/r/man-db/trunk/,
and run ./autogen.sh before starting. You'll need
Autoconf,
Automake, and
Gettext; it is usually
best to install your distribution's packages of these if available. You
may also want to have a copy of
Gnulib handy.
You should read the docs/HACKING file.
There is a mailing list for developers, although it is as yet rather quiet.