Update README.md, centered screenshot!

I think screenshot is better when it is centered.
Merge pull request #85 from MaciejCzyzewski/patch-2

Update README.md, centered screenshot!
Update README.md
Conversion

Adding image files and css changes
Rip out old readme
Merge pull request #2 from xdumaine/gh-pages

Pull in initial version
Merge pull request #3 from xdumaine/master

Pull in initial version