update install links

Created by: sqs

This links to the comprehensive docs for installing, instead of arbitrarily choosing different categories to mention in our blog post vs. our docs. (The blog post had "Local/AWS/DigitalOcean/Kubernetes cluster" vs. the docs' "Single-container server/Docker Compose/Kubernetes". The latter is better IMO.)

It also adds a link to upgrade, which was mentioned in the blog post but was not actually linked.