Documentation: https://devops.wcm.io/conga/plugins/aem/
Issues: https://wcm-io.atlassian.net/projects/WDCONGA
Wiki: https://wcm-io.atlassian.net/wiki/
Continuous Integration: https://travis-ci.com/conga-aem-plugin
Commercial support: https://wcm.io/commercial-support.html
If you want to build from sources make sure you have configured all Maven Repositories in your settings.xml.
See Travis Maven settings.xml for an example with a full configuration.
Then you can build using
mvn clean install