insert images readme.md code example

Example 1: adding a preview image in readme.md

// method 1


// method 2
![Test Image 3](/3DTest.png)
![Test Image 4](https://github.com/tograh/testrepository/3DTest.png 112)

// last method

Example 2: add image to readme

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