Adds CROSS badge to README

[skip ci]

README.md

@@ -5,6 +5,7 @@
 [![codecov](https://codecov.io/gh/systemslab/popper/branch/master/graph/badge.svg)](https://codecov.io/gh/systemslab/popper)
 [![Join the chat at https://gitter.im/systemslab/popper](https://badges.gitter.im/systemslab/popper.svg)](https://gitter.im/falsifiable-us/popper?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![slack](https://img.shields.io/badge/chat-on_slack-C03C20.svg?logo=slack)](https://join.slack.com/t/getpopper/shared_invite/zt-dtn0se2s-c50myMHNpeoikQXDeNbPew)
+[![CROSS](https://img.shields.io/badge/supported%20by-CROSS-green)](https://cross.ucsc.edu)
 
 Popper is a tool for defining and executing container-native workflows 
 in Docker, as well as other container engines. With Popper, you define