Update README.md (#551)

README.md

@@ -65,7 +65,11 @@ Taxonium is structured as a 'monorepo' containing a number of components:
 - [taxonium_backend](./taxonium_backend/) - a server-based backend that allows Taxonium trees to be explored without the user downloading the full tree (N.B. Taxonium can also be used without this backend, with static files acccessed in taxonium_website)
 - [taxonium_data_handling](./taxonium_data_handling/) - this is a node package upon which both the web client and the backend depend (it handles core logic common to both)
 
-## Contributors
+## Contributing
+
+We welcome contributions. We ask that all contributors follow [the Contributor Covenant Code of Conduct](https://github.com/theosanderson/genomium/blob/main/CODE_OF_CONDUCT.md).
+
+### Contributors
 
 Taxonium development was initiated and is led by Theo Sanderson at the Francis Crick Institute.