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
Getting started. Github works.
Revert "Getting started. Github works."

This reverts commit b722036d5144863be3e54653bc8fb726c8ebc5b3.
Merge branch 'gh-pages'

* gh-pages: (31 commits)
  set black translucent bar on the web app
  improve appcache
  shorten links while tweeting, plus to ensure original counts
  remove twitter uri
  remove git.io uri
  shorten links while tweeting, ref #34
  remove space between buttons
  update button id
  fix paypal image name
  add paypal donate button
  restore ga in gh-pages
  Adding a cache manifest
  svg bitcoin icon
  improve bitcoin popup for mobile
  custom bitcoin icon
  improve donate button animation
  add bitcoin donate button
  remove coinwidget
  add basic btc button
  comment out coinwidget
  ...
Release the beast.