2667b642f4
Directing users to use the container repo to install HedgeDoc has caused upgrade-trouble in the past, after we made incompatible changes to the docker-compose.yml in the repo. This commit inserts a minimal docker-compose snipped in the docs, which can be used to get started. Upgrading can then be performed by just incrementing the referenced image version. Signed-off-by: David Mehren <git@herrmehren.de>