[Documentation]: README / examples should include instructions on how to retrieve (& interpret) results of clustering

[crazoter]

Context https://github.com/nmonath/graphgrove/blob/main/examples/clustering.py provides an example on how to do the clustering, but does not actually show how to retrieve the results (e.g. dendrogram) and interpret the results (e.g. how to map the Levels and Nodes back to the original vector matrix)