Documentation request: Address that adding edges one at a time is slower than constructor

[AlexanderJCS]

I had a distance matrix (in csv format) with 50 million edges that I needed to convert into a SimpleWeightedGraph. My first approach was to construct the graph edge-by-edge using the add_edge!(v1, v2, weight) function, however this approach would have taken hours or even days to complete the graph.

In an effort to quickly compute the graph, I used the SimpleWeightedGraph(sources, destinations, weights) constructor. This approach was able to complete the graph in less than one minute.

I am suggesting a documentation change to address the speed of the add_edge!(v1, v2, weight) function and the constructor.

Thank you,
Alexander

[gdalle]

Solved by #38