Change to a non-root user.

[RJSzynal]

If you already have a volume created, this will need to be chown'd to 1000:1000 or the uid/gid overriden at run time

[beberg]

1000:1000 isnt always the right choice. Clarified in READMEs, see issue for explanation.

[RJSzynal]

I would argue that while 1000:1000 isn't always the right choice (nothing is), root is always the wrong choice.
I don't think you can rely on all users to properly read the readme so it is important to ensure the very base defaults are the most secure, especially when it's something that many people around the world will be using to provide charitable help to the cause and perhaps don't have much experience.