[added] separate badges for stable and develop

Reviewers: O2 Material Motion, #material_motion

Tags: #material_motion

Differential Revision: http://codereview.cc/D3476

Author: appsforartists

README.md

@@ -1,7 +1,12 @@
 # Indefinite Observable ##
 
-[![Build Status](https://img.shields.io/circleci/project/github/material-motion/indefinite-observable-js/develop.svg)](https://circleci.com/gh/material-motion/indefinite-observable-js/)
-[![codecov](https://codecov.io/gh/material-motion/indefinite-observable-js/branch/develop/graph/badge.svg)](https://codecov.io/gh/material-motion/indefinite-observable-js)
+<!-- TODO: update version number before releasing -->
+![Current version:](https://img.shields.io/badge/v1.0.0:-222222.svg?logo=npm)
+[![Test status](https://img.shields.io/circleci/project/github/material-motion/indefinite-observable-js/stable.svg?logo=circleci&label=Tests)](https://circleci.com/gh/material-motion/indefinite-observable-js/tree/stable)
+[![Code coverage](https://img.shields.io/codecov/c/github/material-motion/indefinite-observable-js/stable.svg?logo=codecov&logoColor=white&label=Coverage)](https://codecov.io/gh/material-motion/indefinite-observable-js/branch/stable)
+![HEAD:](https://img.shields.io/badge/HEAD:-222222.svg?logo=github&logoColor=white)
+[![Test status](https://img.shields.io/circleci/project/github/material-motion/indefinite-observable-js/develop.svg?logo=circleci&label=Tests)](https://circleci.com/gh/material-motion/indefinite-observable-js/tree/develop)
+[![Code coverage](https://img.shields.io/codecov/c/github/material-motion/indefinite-observable-js/develop.svg?logo=codecov&logoColor=white&label=Coverage)](https://codecov.io/gh/material-motion/indefinite-observable-js/branch/develop)
 
 ## Why? ##