Dev mode setup

[V-Py]

Hello,
I would be glad to help on this project and on some of the issues since I'm having some of them too and using your gantt in my projects.
But I'm having a hard time making the dev mode work correctly since your big update.
Looks like the documentation is not accurate anymore and I don't know how to setup it the right way.
If you or anyone could give the proper way to setup the dev mode it would be awesome so I could do proper PR and help maintain this cool project :)

Thanks