Document how to build pep

[arschmitz]

We need to document, most likely in the readme, how to build pep from the repo and use the examples.

basicly just

1. install node if you have not already link to node binarys
2. install grunt cli if you have not already npm install grunt-cli -g
3. npm install
4. grunt

ref gh-293

[jzaefferer]

Could skip one step by adding grunt-cli to package.json and adding another entry in scripts, then the last step would be npm run build or something like that.