GitHub Preview 
App on Heroku
http://github-preview.herokuapp.com/
Preview script
Put this into your path at e.g. ~/bin/github-preview and chmod +x it.
Then github-preview someproject/Readme.markdown
#!/usr/bin/env ruby
# open a given markdown file via github preview app
raise "gime a file!!" unless ARGV[0]
require 'cgi'
content = File.read(ARGV[0])
url = 'http://github-preview.herokuapp.com/'
exec "open '#{url}/?text=#{CGI.escape content}&format=markdown'"
Local development
bundle
bundle exec rspec spec
bundle exec thin start
open http://localhost:3000
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Using ussy/clippy. Thanks a lot!