Add a proper About page

[noway]

Is your feature request related to a problem? Please describe.
I'm always frustrated when we're linking away to README.md instead of hosting the About page on the actual website.

Describe the solution you'd like
We need an about page with a lot of content for the SEO juice. The history behind us, what service we're providing, all the other useful bits we're putting into README.md atm.

Additional context
We should migrate from using README.md (that should only contain links to CONTRIBUTING.md/"built by"/vaxxnzlocation link sections) for About since that is hosted on GitHub's domain. We need the content to be hosted on vaxx.nz domain to increase domain authority + capture more search queries.

[noway]

@mollyderecourt I think you've been assigned to tackle this by Walt before. Some more context above.