This readme explains the source tree layout.

assembly - The project that creates the distributions.  The following distributions are created:
            (1) geronimo-eclipse-plugin-{version}.zip. 
                This zip is the feature zip distribution that can be extracted directly into ECLIPSE_HOME
            (2) geronimo-update-{version}.zip 
                This zip is can be extract to the local filesystem and used as the local update site to install the feature
            (3) updates/
                This directory is the directory contains the contents for the remote update site.