patch 8.1.2281: 'showbreak' cannot be set for one window

Problem:    'showbreak' cannot be set for one window.
Solution:   Make 'showbreak' global-local.
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 123fd33..738dc7f 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -6748,7 +6748,7 @@
 
 						*'showbreak'* *'sbr'* *E595*
 'showbreak' 'sbr'	string	(default "")
-			global
+			global or local to window |global-local|
 			{not available when compiled without the |+linebreak|
 			feature}
 	String to put at the start of lines that have been wrapped.  Useful
@@ -6765,7 +6765,10 @@
 	Note that tabs after the showbreak will be displayed differently.
 	If you want the 'showbreak' to appear in between line numbers, add the
 	"n" flag to 'cpoptions'.
-
+	A window-local value overrules a global value.  If the global value is
+	set and you want no value in the current window use NONE: >
+		:setlocal showbreak=NONE
+<
 				     *'showcmd'* *'sc'* *'noshowcmd'* *'nosc'*
 'showcmd' 'sc'		boolean	(Vim default: on, off for Unix,
 				       Vi default: off, set in |defaults.vim|)