docs: remove incorrect statement about DIND not working

[agilgur5]

Fixes https://github.com/argoproj/argo-workflows/discussions/13010#discussioncomment-9372559, https://github.com/argoproj/argo-workflows/pull/10778#issuecomment-2105499778

Motivation

As users have mentioned, DIND does still work and the specific DIND image used comes with Docker Engine and so does not rely on the k8s container engine

Modifications

• replace the dockershim note with one about "Alternatives", since DIND is still not as secure

  • use a proper admonition for the note as well, instead of "Note:" with a horizontal rule after

• also follow docs style guide for the rest of the page while at it

  • prefer 1 sentence per line, per style guide
  • use active voice, per k8s style guide
  • simple and direct, per k8s style guide
  • consistently address the user as "you" (instead of using both "you" and "we"), per k8s style guide
  • not in the style guide, but link to GH instead of raw.github as GH is much nicer to read (e.g. syntax highlighting, line numbers, etc etc) and won't auto-download a file on certain browsers (both especially for mobile)

• add a link to the sidecar docs when it is mentioned as well

Verification

make docs passes

[joebowbeer]

Thanks for doing this.