Update server_tuning.rst to include example Imaginary Docker run command

[Kraligor]

-p 9000:9000 is a required flag when running the aio-imaginary container, which I'm sure was mentioned in the past somewhere, but it seems to be gone now

☑️ Resolves
Issue raised by myself in the community: https://help.nextcloud.com/t/my-nextcloud-doesnt-use-aio-imaginary-anymore-and-i-dont-know-why/213234

🖼️ Screenshots

[github-actions]

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