Nukes the quickstart docs, since they were difficult to follow, and
didn't add any value.
Also cleans up the docs, so that we stop having index.md pages that can be
accessed by users, but don't have content.
[*] Restructures the docs to make it easier to find information
[*] Removes information that was spread all over the place
[*] Removes information about cloud installations
[*] Adds docs about system requirements, architecture
[*] Adds docs about HA, backup, restore
[ ] Install
[ ] Upgrade
[ ] Troubleshoot
[ ] CLI, API reference
