TIOCSTI: Document CAP_SYS_ADMIN behaviour in Kconfig

Clarifies that the LEGACY_TIOCSTI setting is safe to turn off even
when running BRLTTY, as it was introduced in commit 690c8b80
("TIOCSTI: always enable for CAP_SYS_ADMIN").
Signed-off-by: Günther Noack <gnoack3000@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Link: https://lore.kernel.org/r/20230808201115.23993-1-gnoack3000@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/Kconfig

@@ -164,6 +164,9 @@ config LEGACY_TIOCSTI
 	  userspace depends on this functionality to continue operating
 	  normally.
 
+	  Processes which run with CAP_SYS_ADMIN, such as BRLTTY, can
+	  use TIOCSTI even when this is set to N.
+
 	  This functionality can be changed at runtime with the
 	  dev.tty.legacy_tiocsti sysctl. This configuration option sets
 	  the default value of the sysctl.