[racket] nightly build available as a ppa

You can now get a nightly build of racket through the Ubuntu PPA system. https://launchpad.net/~plt/+archive/racket-nightly

Here are the quick instructions to set it up

$ sudo apt-get install python-software-properties
$ sudo add-apt-repository ppa:plt/racket-nightly
$ sudo apt-get update
$ sudo apt-get install racket

I'm not quite sure what will happen if you have both the racket ppa and the racket-nightly ppa but probably you shouldn't try it :p. This setup is quite new (as of this week) so let me know if anything doesn't work.