Add imbalanced-learn BibTex citation

[german1608]

First things first, your README.md is pure gold 🥇. I was having a hard time finding good BibTex citations for my academic thesis.

I'm adding the BibTex citation for the imbalanced-learn python package, which aids in dealing with imbalanced datasets.

[german1608]

(And a shameless request if you could label this PR with hacktoberfest-accepted label to this request so it counts for hacktoberfest.com 👀)