Renaming README.txt to README.md & make use of Markdown

Hi,

I've renamed README.txt to README.md and edited the markdown file. I've cleaned up the text in README a bit as well.  I've also added the bash code tag for the commands present in the README, giving it a more cleaner, more readable look.
This makes it more in line with what most will expect from a project on GitHub.
 
Thanks.