patch 9.1.0618: cannot mark deprecated attributes in completion menu

Problem:  cannot mark deprecated attributes in completion menu
Solution: add hl_group to the Dictionary of supported completion fields
          (glepnir)

closes: #15314

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 0d59a2e..e85f341 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -1,4 +1,4 @@
-*insert.txt*    For Vim version 9.1.  Last change: 2024 Jul 13
+*insert.txt*    For Vim version 9.1.  Last change: 2024 Jul 25
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1183,6 +1183,12 @@
 	user_data	custom data which is associated with the item and
 			available in |v:completed_item|; it can be any type;
 			defaults to an empty string
+	hl_group	allows specifying an additional highlight group to
+			apply extra attributes to completion items in the
+			popupmenu. Is combined with |hl-PmenuSel| and
+			|hl-Pmenu| highlighting attributes to apply cterm and
+			gui properties, such as strikethrough to the
+			completion items.
 
 All of these except "icase", "equal", "dup" and "empty" must be a string.  If
 an item does not meet these requirements then an error message is given and