patch 8.1.1280: remarks about functionality not in Vi clutters the help

Problem:    Remarks about functionality not in Vi clutters the help.
Solution:   Move all info about what is new in Vim or already existed in Vi to
            vi_diff.txt.  Remove {not in Vi} remarks. (closes #4268) Add
            "noet" to the help files modeline.  Also include many other help
            file improvements.
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 9b5663e..792a715 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1,4 +1,4 @@
-*index.txt*     For Vim version 8.1.  Last change: 2019 Apr 19
+*index.txt*     For Vim version 8.1.  Last change: 2019 Apr 24
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -862,6 +862,10 @@
 				   position the cursor at the start (left
 				   side) of the screen
 |zt|		zt		   redraw, cursor line at top of window
+|zuw|		zuw		   undo |zw|
+|zug|		zug		   undo |zg|
+|zuW|		zuW		   undo |zW|
+|zuG|		zuG		   undo |zG|
 |zv|		zv		   open enough folds to view the cursor line
 |zw|		zw		   mark word as wrong (bad) spelled word
 |zx|		zx		   re-apply 'foldlevel' and do "zv"