This plugin for QGIS has been discontinued.
GeoServer functionality can now be found in the GeoServer plugin
https://github.com/boundlessgeo/qgis-geoserver-plugin
PostGIS functionality is available in the built-in QGIS DB Manager
Nevertheless, the plugin is documented here.
This repository uses external repositories as submodules. Therefore in order to include the external repositories during cloning you should use the --recursive option:
git clone --recursive http://github.com/boundlessgeo/qgis-suite-plugin.git
Also, to update the submodules whenever there are changes in the remote repositories one should do:
git submodule update --remote