Install documentation

[juliusknorr]

We need to have basic documentation for deb/rpm and docker based installations.

• Write a short introduction for admins around how to setup Euro-Office
• Test run installation on clean vms
• Install the created packages through the repositories and document the process for latest Ubuntu and Rocky Linux
• Write documentation for installing a server from docker
• docs.nextcloud.com: Adapt o rename existing documentation to Nextcloud Office (Collabora)
• docs.nextcloud.com: Copy over install documentation for Nextcloud Office (Euro-Office) (with separate nextcloud office repositories)

Depends on #109

[oleua]

Please, add the documentation how to build your own image of EO.