Markdown updates for README

I made a few improvements to the `README` to make use of [GitHub Flavored Markdown](https://help.github.com/articles/github-flavored-markdown) for both readability and maintainability. I removed some unnecessary `<br />` tags and used [fenced code blocks](https://help.github.com/articles/github-flavored-markdown#fenced-code-blocks) to highlight the command line interaction. I hope you'll find it useful....

|Before|After|
|---|---|
|
![image](https://f.cloud.github.com/assets/121322/2002053/aa58d1aa-85de-11e3-9f4c-20aa80438920.png)|![image](https://f.cloud.github.com/assets/121322/2002048/7fa1c642-85de-11e3-8f07-bde9eb98ec39.png)|

Cheers,
  Lee :beers:

**cc:** @brettin