Adicionar premissa para o ruby-bundler (Ubuntu) no Readme

[brfso]

bundle install
The program 'bundle' can be found in the following packages:

• bundler
• ruby-bundler
  Try: sudo apt-get install

[chulao]

No caso do OSX o erro que dá é:
./install.sh: line 15: bundle: command not found

E para instalar o bundler:

sudo gem install bundler