Missing rtd style file

[ClaraBuettner]

Since an update of rtd, a new configuration file for the style is needed. As long is that is not added, the rtd looks different than intended. I fixed the same problem in etrago and will implement it in egon-data as well.

[ClaraBuettner]

I can compile it locally without any problems and would like to try it out online. @IlkaCu Can you add me to the rtd of egon-data?

[IlkaCu]

Done