Proposal to add CONTRIBUTING.md

[adamazad]

At the moment, there is no CONTRIBUTING.md file. I propose to create a one indicating how to add new reports via issues (template) or a PR.

If we use Gatsby, the steps are as follows:

1. Fork this repo
2. Create a new branch.
3. Edit src/pages/historic-attacks.mdx. It is a markdown file. Add your record to the table.
4. Once, finished, create a PR against this repo.

Of course, you are welcome to open a new issue to report attacks, propose changes, and improve the initiative.

[PatrickAlphaC]

Agreed. We can split the contributing docs to their own section.

[adamazad]

As addressed in #4