add images to readme code example

Example 1: add image to readme

![alt text](http://url/to/img.png)

Example 2: github readme.md add image

![GitHub Logo](/images/logo.png)
Format: ![Alt Text](url)

Example 3: add image to readme

![alt text](https://github.com/[username]/[reponame]/blob/[branch]/image.jpg?raw=true)