Provide a BibTeX to ease citing of pypowsybl

[sylvlecl]

• Do you want to request a feature or report a bug?

Feature/doc

• What is the motivation / use case for changing the behavior?

Researchers usually use BibTeX format to reference any used material in their work (other papers, books, etc). It would be useful to provide one for pypowsybl in order to make its mention easier in such work. See for example for pandapower