patch 8.2.3874: cannot highlight the number column for a sign

Problem:    Cannot highlight the number column for a sign.
Solution:   Add the "numhl" argument. (James McCoy, closes #9381)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 3e71ba1..b4e7761 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -5601,8 +5601,8 @@
 	number.
 	When a long, wrapped line doesn't start with the first character, '-'
 	characters are put before the number.
-	See |hl-LineNr|  and |hl-CursorLineNr| for the highlighting used for
-	the number.
+	For highlighting see |hl-LineNr|, and |hl-CursorLineNr|, and the
+	|:sign-define| "numhl" argument.
 						*number_relativenumber*
 	The 'relativenumber' option changes the displayed number to be
 	relative to the cursor.  Together with 'number' there are these