docs: add doom-docs-mode & doom-docs-org-mode

These two modes exist to provide a nicer reading experience while
viewing Doom's org documentation from within Emacs; they hide
meta-lines, comments, markup, and more.

They also enable our docs to use IDs for links and keep our ID db
separate from any user ID dbs.

core/autoload/help.el

@@ -739,3 +739,4 @@ Uses the symbol at point or the current selection, if available."
                                    (format "%s.el" filebase)))
             collect it)
    query "Search loaded files: "))
+