The Debian package of propellor ships its full source code because propellor is configured by rebuilding it, and embraces modification of any of the source code. /usr/bin/propellor is a wrapper which will set up a propellor git repository in ~/.propellor/, and run ~/.propellor/propellor if it exists. Edit ~/.propellor/config.hs to configure it. Note that upgrading the propellor package will not update your ~/.propellor/ repository. You can `git pull upstream` in your repository to update to the current upstream source, as distributed in the Debian package. Older versions of propellor set the upstream remote to point to a repository on github, so if you used one of them, you may want to change it to point to the new location, /usr/src/propellor/