Update code of conduct

[Potherca]

This MR moves the code of conduct from CONTRIBUTING.md into a separate file, updates the code-of-conduct to Contributor Covenant v2 and replaces Frencks email with my own for reporting issues.

It also adds a Contributor Covenant badge to README file, to show we adhere to the covenant.

[jrfnl]

Two remarks:

• For GH to pick up on the file automatically, it should be called CODE_OF_CONDUCT.md (underscores, not dashes).
• As we already have a .github directory in place, I'd like to suggest moving the file there. That's a fully supported location.

Also see: https://docs.github.com/en/github/building-a-strong-community/adding-a-code-of-conduct-to-your-project

[Potherca]

For GH to pick up on the file automatically, it should be called CODE_OF_CONDUCT.md (underscores, not dashes).

Yeah, that's a derp on my side.

As we already have a .github directory in place, I'd like to suggest moving the file there. That's a fully supported location.

I personally prefer having the file in the root, making it possible to link to it from markdown (and on Github Pages if/when they are used).