[ changelog ] Write about new option

CHANGELOG.md

@@ -1,7 +1,6 @@
 Release notes for Agda version 2.6.2
 ====================================
 
-
 Pragmas and options
 -------------------
 
@@ -10,3 +9,9 @@ Pragmas and options
   enabled, Agda will only consider candidates for instance search that
   are in scope under an unqualified name (see
   [#4522](https://github.com/agda/agda/pull/4522)).
+
+* New option `--highlight-occurrences` (off by default) enables the HTML
+  backend to include a JavaScript file that highlights all occurrences of
+  the mouse-hovered symbol (see
+  [#4535](https://github.com/agda/agda/pull/4535)).
+