Add a reference to cite and license

[jpssrocha]

Hi,

i've been using this code base and it's helping a lot!

Me and some colleagues are using it. In some time we will be able to publish some articles with results we've got with the help of this code. So it would be cool if a way to cite this code were added here ...

I believe that zenodo can be used for that:

https://about.zenodo.org/

Another detail to add is the license. So people is sure that it is ok to use this code hehe

Thanks for the attention.