Make links to the sources more obvious

[kastl-ars]

Issue description

Is it just me or does the home page scm-manager.org not contain a link to the actual source code at https://github.com/scm-manager/scm-manager? It might be a good idea to add a link for the people interested in the actual code.

Also https://scm-manager.org/download/ does not contain links to the sources.

Kind Regards,
Johannes

[pfeuffer]

Good point, we will talk about this.