Improve Readme

[tuhinmallick]

add sample codes for each feature usage.

[KonradUdoHannes]

There are r markdown files with examples but so far the README does not make a clear reference to this. I think a combination of stating some functionality in the readme and refering to the r markdown files would be a good combination. This will not bloat the readme too much, but still help potential users to get a feeling for the project.