patch 8.1.1431: popup window listed as "Scratch"

Problem:    Popup window listed as "Scratch".
Solution:   List them as "Popup".
diff --git a/runtime/doc/windows.txt b/runtime/doc/windows.txt
index 187d00e..dca9dbf 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -1,4 +1,4 @@
-*windows.txt*   For Vim version 8.1.  Last change: 2019 May 18
+*windows.txt*   For Vim version 8.1.  Last change: 2019 May 30
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1030,6 +1030,13 @@
 		thus you can always go to a specific buffer with ":buffer N"
 		or "N CTRL-^", where N is the buffer number.
 
+		For the file name these special values are used:
+			[Prompt]	|prompt-buffer|
+			[Popup]		buffer of a |popup-window|
+			[Scratch]	'buftype' is "nofile"
+			[No Name]	no file name specified
+		For a |terminal-window| buffer the status is used.
+
 		Indicators (chars in the same column are mutually exclusive):
 		u	an unlisted buffer (only displayed when [!] is used)
 			   |unlisted-buffer|