Add docs about docker requirements / surface better error if docker compose plugin is not installed

[MalteJanz]

Technical TODO

Encountered the following issue on my system, running these steps:

• shopware-cli project create and choose docker
• shopware-cli project dev fails to start docker containers with an error:

unknown shorthand flag: 'd' in -d

Failed: exit status 125

That error message is not very descriptive, turns out I didn't had the docker compose plugin installed on my system yet. I would suggest to do either or both:

• document the docker + docker compose plugin system requirement when you want to run projects using docker
• provide a better error on startup that clearly says you don't have the docker compose plugin

Additional context:

• MacOS 26.6.2
• colima version 0.10.3 with runtime: docker
• Docker Engine - Community (Client 29.8.1, Server 27.4.0)
• (after fixing the issue) Docker Compose version 5.5.1