Improve getting started documentation guide.

[hellsworth]

I've moved the original getting-started.md to a new folder that now contains a README.md. The README.md provides a high level of how to contribute, with links to existing resources.

[LevitatingBusinessMan]

If I understand gitbook correctly these pages should switch places, right?

Because now when the userlands on the front-page, and they use the link on the front-page or the left-side menu to navigate to "Getting Started" they will end up on a page titled "Setting up a build environment". While the left-side menu drops down to show another "Getting Started" page which is where they should've landed.

So the README.md should contain the generic getting started text while the build instructions should move to getting-started/setting-up-a-build-environment.md.

However I can't actually compile the gitbook because my node version is 10 major versions too high to run gitbook-cli, so I haven't been able to test it properly.

Edit: Doesn't seem like it's possible to compile this gitbook locally at all, even with a working node version. So I can't preview it.

[hellsworth]

Yeah you're absolutely right! I had the naming backwards but I've fixed it now.
Unfortunately, I also do not have a way to preview this.. so I hate to test in production but let's merge it. If it's terrible, we can always revert 😅