[Docs] Annotate gtk-doc formatting with some un-annotated (out)s.

src/hb-ot-layout.cc

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 381c69a..f7006df 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -497,8 +497,8 @@
  * @face: #hb_face_t to work upon
  * @table_tag: HB_OT_TAG_GSUB or HB_OT_TAG_GPOS
  * @script_tags: Array of #hb_tag_t script tags
- * @script_index: The index of the requested script tag
- * @chosen_script: #hb_tag_t of the script tag requested
+ * @script_index: (out): The index of the requested script tag
+ * @chosen_script: (out): #hb_tag_t of the script tag requested
  *
  * Deprecated
  **/
@@ -506,8 +506,8 @@
 hb_ot_layout_table_choose_script (hb_face_t      *face,
 				  hb_tag_t        table_tag,
 				  const hb_tag_t *script_tags,
-				  unsigned int   *script_index,
-				  hb_tag_t       *chosen_script)
+				  unsigned int   *script_index  /* OUT */,
+				  hb_tag_t       *chosen_script /* OUT */)
 {
   const hb_tag_t *t;
   for (t = script_tags; *t; t++);