[fallback] Add TODO note

src/hb-fallback-shape.cc

@@ -95,6 +95,16 @@ _hb_fallback_shape (hb_shape_plan_t    *shape_plan HB_UNUSED,
 		    const hb_feature_t *features HB_UNUSED,
 		    unsigned int        num_features HB_UNUSED)
 {
+  /* TODO
+   *
+   * - Apply fallback kern.
+   * - Handle Variation Selectors?
+   * - Apply normalization?
+   *
+   * This will make the fallback shaper into a dumb "TrueType"
+   * shaper which many people unfortunately still request.
+   */
+
   hb_codepoint_t space;
   font->get_glyph (' ', 0, &space);