docs: Port new text to individual highlighters' documentation.

The new text is from the preceding two commits, 22123ab622 + ded1c8789b.

Fixes a broken link.

docs/highlighters/root.md

@@ -16,5 +16,8 @@ for example in `~/.zshrc`:
 
     ZSH_HIGHLIGHT_STYLES[root]='bg=red'
 
-The syntax for declaring styles is documented in [the `zshzle(1)` manual
-page](http://zsh.sourceforge.net/Doc/Release/Zsh-Line-Editor.html#SEC135).
+The syntax for values is the same as the syntax of "types of highlighting" of
+the zsh builtin `$zle_highlight` array, which is documented in [the `zshzle(1)`
+manual page][zshzle-Character-Highlighting].
+
+[zshzle-Character-Highlighting]: http://zsh.sourceforge.net/Doc/Release/Zsh-Line-Editor.html#Character-Highlighting