Standardize documentation for extended config
Standardize documentation for extended config

This patch adds parameter/explanation tables for the two other commands
that support extended configuration syntaxes, so now we have
identically-formatted tables for link, shell, and clean.

This change was prompted by
https://github.com/anishathalye/dotbot/issues/223.

anishathalye/dotbot,anishathalye/dotbot