doc: use consistent indenting for unordered list items

Address Markdownlint MD007 rule.
Default suggestion is 2 space indenting for unordered list items.

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>