Added colors for sfood-graph

[gaurav281296]

Hey, I really liked your utility and found it useful for my project.
I noticed that the graphs can become very complicated when there are a lot of imports across modules.

I have added a random color (high contrasts) to each edge of the graphviz file so that it is easier to trace the source node to the destination node.

You can look into it here:

https://github.com/gaurav281296/snakefood