doc: start unorded lists at start of line

Address Markdownlint MD006 rule.
Can flag when list items aren't indented far enough.

PR-URL: https://github.com/nodejs/node/pull/29390


Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>