First, all you need it to install git and node.js. Then, you do the following :
git submodule add git://github.com/dsimard/ready.js.git ready.js
cd ready.js && git submodule init && git submodule update && cd ..
Create config file in your_project/ready.conf.js :
echo 'node ready.js/ready.js ready.conf.js' >> .git/hooks/pre-commit
Then, every time you commit, ready.js will be run. You can see alternative installations on the github page.
Try Ready.js today!