Improve README file

[cmurray3]

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This improvement was suggested by one of the extremely helpful reviewers of the paper titled "VeRoViz: A Vehicle Routing Visualization Toolkit" (https://dx.doi.org/10.2139/ssrn.3746037). See also #36, #37, #38, #39, and #40.

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• Add information from https://veroviz.org/about.html
• Add a section describing how people can contribute.

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The original reviewer comment appears below:

To aid with the contributing I suggest ... [a] more elaborate README file: most of the information is all already included in the webpages, however I think it helps to repeat it in the repository as well. Particularly,

• Contact details
• Contributing guidelines (how you'd want people to contribute to the project)