Add Raspberry Pi Tutorial

[mhellmeier]

I wrote a tutorial on how to use and install the PSA Car Controller on a Raspberry Pi and added it to the README.md.

[stevoh6]

If you are author of the article, also citroen eC4 and eBerlingo are part of the same psa family :-)

[mhellmeier]

Thanks a lot for the hint, @stevoh6! Citroën and many more brands are mentioned in the first paragraph of the solution part.

[flobz]

thanks for this tutorial !