Update Docker instructions for 0.5.3 and avoid `git clone`
Update Docker instructions for 0.5.3 and avoid `git clone`

Since 0.5.3 Docker listens on a socket which is only readable/writeable by `root`, all `docker` commands need to be run as a superuser.

It is also possible to build from GitHub without cloning so this pull includes that change as well.

Tested and works on Ubuntu 13.04 with lxc-docker 0.5.3 from official Launchpad PPA.
gsamokovarov/web-console,zBMNForks/web-console,gsamokovarov/web-console-rails3,rails/web-console,gsamokovarov/web-console-rails3,gsamokovarov/web-console,zBMNForks/web-console,tabislick/web-console,eileencodes/web-console,jmbejar/web-console,jmbejar/web-console,tabislick/web-console,slobodankovacevic/web-console,zBMNForks/web-console,sh19910711/web-console,sh19910711/web-console,zBMNForks/web-console,slobodankovacevic/web-console,ryandao/web-console,gsamokovarov/web-console,sh19910711/web-console,tabislick/web-console,ryandao/web-console,eileencodes/web-console,ryandao/web-console,gsamokovarov/web-console-rails3,jmbejar/web-console,rails/web-console,eileencodes/web-console,tabislick/web-console,eileencodes/web-console,sh19910711/web-console,rails/web-console,gsamokovarov/web-console,rails/web-console