Add citation to README.md (#81)

* Add citation to README.md

* Adding note to citation section

Co-authored-by: Alex Zook <zook.ae+github@gmail.com>

Co-authored-by: Alex Zook <zook.ae+github@gmail.com>

README.md

 
 ## License
 * [License](com.unity.perception/LICENSE.md)
+
+## Citation
+If you find this package useful, consider citing it using:
+```
+@misc{com.unity.perception2020,
+    title={Unity {P}erception Package},
+    author={{Unity Technologies}},
+    howpublished={\url{https://github.com/Unity-Technologies/com.unity.perception}},
+    year={2020}
+}
+```