talk guest room integration

[Talk.ai](https://talk.ai) is a slack like IM application, it support some features like group chat, robot support, and website integrations.

Recently it allows the user to visit topics as 'guest', so I need a badge to put these urls on my github pages or any other sites. For example, the badge of 'http://img.shields.io/talk/9c81ff703b.svg' should look like ![talk](http://img.shields.io/badge/talk-node--sdk-blue.svg).

This pull request add the talk integration