Add README

It would be cool to have a description of this repository?
As I understood, this documents an API to query data from the ladesäulenregister used for a map?

If I am correct, the same ladesäulenregister is also available as CSV as a whole at
https://www.bundesnetzagentur.de/SharedDocs/Downloads/DE/Sachgebiete/Energie/Unternehmen_Institutionen/E_Mobilitaet/Ladesaeulenregister_CSV.csv?__blob=publicationFile&v=42

This is used at our research institut like this: https://github.com/NOWUM/open-energy-data-server/blob/main/crawler/ladesaeulenregister.py

Review the repository's API implementation and the linked ladesäulenregister.py example to confirm what the project does and how the Bundesnetzagentur data is used. Add a README describing the repository and API, including the relevant data source; the work is done when a new reader can understand the project's purpose.

Written by the indexing model from the issue text.