[MERGE #77] Update README - add gitter
[MERGE #77] Update README - add gitter

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

Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,arunetm/ChakraCore_0114,mrkmarron/ChakraCore,arunetm/ChakraCore_0114,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,arunetm/ChakraCore_0114,arunetm/ChakraCore_0114,mrkmarron/ChakraCore,arunetm/ChakraCore_0114,mrkmarron/ChakraCore,arunetm/ChakraCore_0114,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore