"How to Contribute" page update Markdown

[dxc3452]

Hello,

Here is the markdown page for the "How to Contribute" page you wanted us to do.

I didn't know how to convert the markdown files into the html page for how to contribute.
Located here: https://github.com/VulnerabilityHistoryProject/vulnerability-history/blob/master/app/views/contribute/index.html.erb

I attached the files to this issue. The pictures go with the markdown page.

curationguide.md