[docs] Add CII Best Practices (mui#8736)

README.md

@@ -10,6 +10,7 @@ that you can use to tag your questions.
 [![CircleCI](https://img.shields.io/circleci/project/github/callemall/material-ui/v1-beta.svg)](https://circleci.com/gh/callemall/material-ui/tree/v1-beta)
 [![Gitter](https://img.shields.io/badge/gitter-join%20chat-f81a65.svg)](https://gitter.im/callemall/material-ui?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Coverage Status](https://img.shields.io/codecov/c/github/callemall/material-ui/v1-beta.svg)](https://codecov.io/gh/callemall/material-ui/branch/v1-beta)
+[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1320/badge)](https://bestpractices.coreinfrastructure.org/projects/1320)
 
 [![PeerDependencies](https://img.shields.io/david/peer/callemall/material-ui.svg)](https://david-dm.org/callemall/material-ui#info=peerDependencies&view=list)
 [![Dependencies](https://img.shields.io/david/callemall/material-ui.svg)](https://david-dm.org/callemall/material-ui)