This just brings the documentation for these commands more inline with
other deprecations, plus offers a link to the recommended alternative
as well as the explanation for deprecation
What we have at the moment isn't really the same as TiddlyWiki
classic's shadow tiddlers, it's a much simpler system for excluding
tiddlers. We'll use the term "shadow" instead to refer to the way that
tiddlers in plugins behave, which is exactly like TiddlyWiki classic's
shadow tiddlers.