add citation file

[FelipeMartins96]

https://docs.github.com/pt/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files

depending on how it works, se if it can substitute:

rSoccer/README.md

Lines 5 to 18 in 17f7640

	## Reference
	If you use this environment in your publication and want to cite it, utilize this BibTeX:
	```
	@misc{martins2021rsoccer,
	title={rSoccer: A Framework for Studying Reinforcement Learning in Small and Very Small Size Robot Soccer},
	author={Felipe B. Martins and Mateus G. Machado and Hansenclever F. Bassani and Pedro H. M. Braga and Edna S. Barros},
	year={2021},
	eprint={2106.12895},
	archivePrefix={arXiv},
	primaryClass={cs.LG}
	}
	```