patch 8.2.2366: when using ":sleep" the cursor is always displayed

Problem:    When using ":sleep" the cursor is always displayed.
Solution:   Do not display the cursor when using ":sleep!". (Jeremy Lerner,
            closes #7688)
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index 91d22de..aec4ca0 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1590,6 +1590,8 @@
 |:sign|		:sig[n]		manipulate signs
 |:silent|	:sil[ent]	run a command silently
 |:sleep|	:sl[eep]	do nothing for a few seconds
+|:sleep!|	:sl[eep]!	do nothing for a few seconds, without the
+				cursor visible
 |:slast|	:sla[st]	split window and go to last file in the
 				argument list
 |:smagic|	:sm[agic]	:substitute with 'magic'