os/signal: add Notify windows documentation

Add that Notify only accepts os.Interrupt signal on windows.

Updates #77076

Change-Id: I09a3ae68d198d615f12ee7de6082c4993f39f140
Reviewed-on: https://go-review.googlesource.com/c/go/+/770920
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

Author: alexbrainman

src/os/signal/doc.go

@@ -213,8 +213,9 @@ before raising the signal.
 On Windows a ^C (Control-C) or ^BREAK (Control-Break) normally cause
 the program to exit. If Notify is called for [os.Interrupt], ^C or ^BREAK
 will cause [os.Interrupt] to be sent on the channel, and the program will
-not exit. If Reset is called, or Stop is called on all channels passed
-to Notify, then the default behavior will be restored.
+not exit. [os.Interrupt] is the only signal that can be used on Windows.
+If Reset is called, or Stop is called on all channels passed to Notify,
+then the default behavior will be restored.
 
 Additionally, if Notify is called, and Windows sends CTRL_CLOSE_EVENT,
 CTRL_LOGOFF_EVENT or CTRL_SHUTDOWN_EVENT to the process, Notify will