runtime(doc): more clarification for the :keeppatterns needed

Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: chrisbra

runtime/doc/cmdline.txt

@@ -1,4 +1,4 @@
-*cmdline.txt*   For Vim version 9.1.  Last change: 2024 Aug 16
+*cmdline.txt*   For Vim version 9.1.  Last change: 2024 Aug 19
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -379,7 +379,8 @@ terminals)
 
 :keepp[atterns] {command}			*:keepp* *:keeppatterns*
 		Execute {command}, without adding anything to the search
-		history or modifying the last substitute string for |:&|.
+		history and, in case of the the |:s| and |:&| command, without 
+		modifying the last substitute pattern and substitute string.
 
 ==============================================================================
 2. Command-line completion				*cmdline-completion*