Add ability to override command for main container

[tomaszkiewicz]

This simple change adds ability to override entrypoint for the container.

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Story behind the change: (if someone is interested or have similar issue)

I encountered strange issue while using volumes based on NFS as a storage for n8n and n8n was unable to execute entrypoint script due to immutable .snapshot directory on the mounted filesystem, so the only way to temporary hack it was to override entrypoint with my own version that does chown optionally and runs as root:

          command:
            - tini
            - --
            - /bin/sh
            - -c
            - chmod o+rx /root; chown -R node /root/.n8n || true; chown -R node /root/.n8n; ln -s /root/.n8n /home/node; chown -R node /home/node || true; node /usr/local/bin/n8n

[Vad1mo]

looks good to me. Can be accepted.

Please also update the README file

[tomaszkiewicz]

For some strange reason GH doesn't see new commit and doesn't allow me to open another PR for the same branch... but I also got error that they're under heavy load, so let's wait and see if the commit will show up soon.

[Vad1mo]

@tomaszkiewicz ping