add a markdown image code example

Example 1: markdown image

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

Example 2: markdown add image

Here's our logo (hover to see the title text):

Inline-style: 
![alt text](https://github.com/adam-p/markdown-here/raw/master/src/common/images/icon48.png "Logo Title Text 1")

Reference-style: 
![alt text][logo]

[logo]: https://github.com/adam-p/markdown-here/raw/master/src/common/images/icon48.png "Logo Title Text 2"