patch 8.1.1882: cannot specify properties of the info popup window

Problem:    Cannot specify properties of the info popup window.
Solution:   Add the 'completepopup' option.  Default to PmenuSel highlight.
diff --git a/runtime/doc/insert.txt b/runtime/doc/insert.txt
index 852ba68..8ba360b 100644
--- a/runtime/doc/insert.txt
+++ b/runtime/doc/insert.txt
@@ -1,4 +1,4 @@
-*insert.txt*    For Vim version 8.1.  Last change: 2019 May 07
+*insert.txt*    For Vim version 8.1.  Last change: 2019 Aug 18
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1092,7 +1092,7 @@
 	menu		extra text for the popup menu, displayed after "word"
 			or "abbr"
 	info		more information about the item, can be displayed in a
-			preview window
+			preview or popup window
 	kind		single letter indicating the type of completion
 	icase		when non-zero case is to be ignored when comparing
 			items to be equal; when omitted zero is used, thus
@@ -1114,11 +1114,22 @@
 
 The "menu" item is used in the popup menu and may be truncated, thus it should
 be relatively short.  The "info" item can be longer, it will  be displayed in
-the preview window when "preview" appears in 'completeopt'.  The "info" item
-will also remain displayed after the popup menu has been removed.  This is
-useful for function arguments.  Use a single space for "info" to remove
-existing text in the preview window.  The size of the preview window is three
-lines, but 'previewheight' is used when it has a value of 1 or 2.
+the preview window when "preview" appears in 'completeopt' or in a popup
+window when "popup" appears in 'completeopt'.  In the preview window the
+"info" item will also remain displayed after the popup menu has been removed.
+This is useful for function arguments.  Use a single space for "info" to
+remove existing text in the preview window.  The size of the preview window is
+three lines, but 'previewheight' is used when it has a value of 1 or 2.
+
+						*complete-popup*
+When "popup" is in 'completeopt' a popup window is used to display the "info".
+Then the 'completepopup' option specifies the properties of the popup.  The
+option is a comma separated list of values:
+	height		maximum height of the popup
+	width		maximum width of the popup
+	highlight	highlight group of the popup (default is Pmenu)
+Example: >
+	:set completepopup=height:10,width:60,highlight:InfoPopup
 
 The "kind" item uses a single letter to indicate the kind of completion.  This
 may be used to show the completion differently (different color or icon).