[MERGE #77] Update README - add gitter

Merge pull request #77 from liminzhu:docs
Add gitter in Contact us section.

README.md

@@ -83,4 +83,4 @@ Please refer to [Contribution guidelines](CONTRIBUTING.md) and the [Code of Cond
 For details on our planned features and future direction please refer to our [roadmap](https://github.com/Microsoft/ChakraCore/wiki/Roadmap).
 
 ## Contact us
-For questions about ChakraCore, please open an [issue](https://github.com/Microsoft/ChakraCore/issues/new) and prefix the issue title with [Question].
+For questions about ChakraCore, you can reach us on [Gitter](https://gitter.im/Microsoft/ChakraCore) or open an [issue](https://github.com/Microsoft/ChakraCore/issues/new) and prefix the issue title with [Question].