Update with examples

Hello,

I am not an expert in coding with JS, and I have confusion in how to call functionalities I see in vivagraph.js.

Would it be possible to add examples on the wiki for advanced features?
e.g. get a position of a node element : (I gfindElementPosition ? or getNodePosition ? graph.getNodePosition(4114904) ? )

apply betweeness and other centralities?

how to be notified when graph is relaxed (or stop computation after N iterations, and notify, so to perform other functionalities only when clearer position of nodes...): is it maybe "isStable" property of renderer function?

Start with the wiki and the graph and renderer entry points mentioned in the issue, including graph.getNodePosition and the possible isStable property. Review how node positions, centrality calculations, and layout relaxation are currently exposed. Done means adding clear examples for the requested advanced features and documenting how to detect or limit layout computation.

Written by the indexing model from the issue text.