Add required --root to ./run_docker` build from source documentation

[goulashsoup]

Description

It seems --root option is required when running make in the docker container, see #4753

Checklists

• Add new / update outdated documentation

[hoodmane]

Well it's not required in general, there is something specific to the way permissions are working on your machine that is breaking it without it. I wouldn't really recommend this either because it has the annoying consequence that all the build artifacts are owned by root and you have to use sudo to remove them.

[hoodmane]

But thanks for the PR @goulashsoup. How about instead adding the comment that if you see permissions problems when building, passing --root to run_docker can help?

[goulashsoup]

But thanks for the PR @goulashsoup. How about instead adding the comment that if you see permissions problems when building, passing --root to run_docker can help?

Can do that as well...

[goulashsoup]

@hoodmane Changed it.

[hoodmane]

Thanks!