docs: add quickstart and prologue

[priyashpatil]

Adds quick start guide and restructure the docs with prologue.

closes #542

[jaydrogers]

Thanks for this! Will review and will keep you posted 👍

[jaydrogers]

I appreciate your efforts on this, but during the v4 rewrite we rewrote the docs site and restructured a ton of content.

I added an example here: https://280-create-a-frankenphp-vari.serversideup-php.pages.dev/open-source/docker-php/docs/getting-started/installation

I'll take more PRs on the #283 branch if you think there are any other improvements that should be added.

I greatly appreciate your time and I look forward to seeing more PRs from you in the future