Replaced ReadMe.txt with README.md
Added CONTRIBUTING.md

md is Markdown format
https://help.github.com/articles/github-flavored-markdown

How CONTRIBUTING.md works on GitHub:
https://github.com/blog/1184-contributing-guidelines
Merge pull request #35 from rlove/feature/MarkdownFiles

Replaced ReadMe.txt with README.md and Added CONTRIBUTING.md