add documentation for the theme workflow

[schleichardt]

• checking in jars in the lib folder can be challenging in a team and with pull requests
• maybe make some suggestions how to publish it to a team accessible thing, maybe already a file server is sufficient

[selo-ecube]

Maybe I'm too chatty with this comment, but why is this libs/ folder mechanism provided anyways?

If someone considers checking in Jar files into Git and finds that problematic (which it is) - shouldn't they consider using Nexus or just use Maven deploy via ftp to host a Maven repository or something similar?

[schleichardt]

yes, exactly