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. This is because you may have local changes to the source, or may need to adapt your config.hs to work with the new version of propellor. Instead, if your ~/.propellor/ is from an older version of propellor, /usr/bin/propellor will warn that it's out of date, and tell you how to merge in the changes.