Document how to write files to host as non-root

[alyssadai]

Given that we mount host directories to the container in several of our tools/services (e.g., graph, CLI) and create files on the host as a result, we should provide a workaround to write these files not as root (default), so that users can easily modify or delete them on the host afterwards if needed without permission issues.

As a starting point, see: https://hackmd.io/@neurobagel/HyGSQ-Ip6#Running-Docker-container-as-non-root-user

[github-actions]

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