docs: Restore (with changes) links removed in f5ca4b891b.

The preceding commit, which made docs/highlighters.md and
highlighters/README.md distinct, allows reverting their removal.

docs/highlighters.md

@@ -3,12 +3,19 @@ zsh-syntax-highlighting / highlighters
 
 Syntax highlighting is done by pluggable highlighters:
 
-* `main` - the base highlighter, and the only one active by default.
-* `brackets` - matches brackets and parenthesis.
-* `pattern` - matches user-defined patterns.
-* `cursor` - matches the cursor position.
-* `root` - highlights the whole command line if the current user is root.
-* `line` - applied to the whole command line
+* `main` - the base highlighter, and the only one [active by default][1].
+* `brackets` - [matches brackets][2] and parenthesis.
+* `pattern` - matches [user-defined patterns][3].
+* `cursor` - matches [the cursor position][4].
+* `root` - highlights the whole command line [if the current user is root][5].
+* `line` - applied to [the whole command line][6].
+
+[1]: highlighters/main.md
+[2]: highlighters/brackets.md
+[3]: highlighters/pattern.md
+[4]: highlighters/cursor.md
+[5]: highlighters/root.md
+[6]: highlighters/line.md
 
 
 How to activate highlighters