patch 8.2.3465: cannot detect insert scroll mode

Problem:    Cannot detect insert scroll mode.
Solution:   Add "scroll" to complete_info(). (closes #8943)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 43aae40..588f511 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -3883,6 +3883,8 @@
 		   ""		     Not in completion mode
 		   "keyword"	     Keyword completion |i_CTRL-X_CTRL-N|
 		   "ctrl_x"	     Just pressed CTRL-X |i_CTRL-X|
+		   "scroll"	     Scrolling with |i_CTRL-X_CTRL-E| or
+				     |i_CTRL-X_CTRL-Y|
 		   "whole_line"	     Whole lines |i_CTRL-X_CTRL-L|
 		   "files"	     File names |i_CTRL-X_CTRL-F|
 		   "tags"	     Tags |i_CTRL-X_CTRL-]|