Added Mill to supporting tools section (#11)

Author: lefou

README.md

@@ -19,6 +19,7 @@ We only extended the concept to project repositories.
 - [ansible-lint](https://github.com/ansible/ansible-lint)
 - [ansible-navigator](https://github.com/ansible/ansible-navigator)
 - [doc8](https://github.com/PyCQA/doc8)
+- [Mill](https://github.com/com-lihaoyi/mill)
 - [molecule](https://github.com/ansible-community/molecule)
 
 ## Q&A