patch 8.1.2192: cannot easily fill the info popup asynchronously

Problem:    Cannot easily fill the info popup asynchronously.
Solution:   Add the "popuphidden" value to 'completeopt'. (closes #4924)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 8436c8a..e62ee89 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 8.1.  Last change: 2019 Sep 28
+*options.txt*	For Vim version 8.1.  Last change: 2019 Oct 20
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -1919,6 +1919,13 @@
 		    See |'completepopup'| for specifying properties.
 		    {only works when compiled with the |+textprop| feature}
 
+	   popuphidden
+	   	    Just like "popup" but initially hide the popup.  Use a
+		    |CompleteChanged| autocommand to fetch the info and call
+		    |popup_show()| once the popup has been filled.
+		    See the example at |complete-popuphidden|.
+		    {only works when compiled with the |+textprop| feature}
+
 	   noinsert Do not insert any text for a match until the user selects
 		    a match from the menu. Only works in combination with
 		    "menu" or "menuone". No effect if "longest" is present.