title: Sigma.js learning and examples
body: <p>I would like to discover sigma.js so I might use it in a project.
  I know already a little of d3 but through searching on the internet people
  mention that sigma is better for graphs and in my case , for example in graph 
  databases sigma might be better. But I searched and I couldn't find a lot documentation about sigma or any tutorials. Even the examples in jacomy's website doesn't exist. Could someone advice me on where to start in order to learn sigma.js? </p>