add documentation how to get it running locally (without opening NC to the public)

[szaimen]

two options:

1. run aio behind a reverse proxy only open port 80, the domain that you want to use needs to point to your public ip-address, do not open port 443, set up a dns-server like pi-hole and use it as dns-server in your network, set a custom dns record for this domain and point it to the internal ip-address of your reverse proxy, (set the dns-server in docker-config.json to the internal ip of the dns server - not neccessarily needed) -> now everything should work.
2. use dns-challenge with e.g. caddy as revers proxy, set up a local ip-address as a-record for your domain, disable dns-rebind-protection for this domain in your router settings -> should work as well.
3. use cloudflare? (but basically it is open to the public then but will work in situations where you are not in control over the network)

[szaimen]

I've added some documentation on this here https://github.com/nextcloud/all-in-one/blob/enh/878/run-locally/local-instance.md. Testing and feedback is welcome!