sapi: add reference to script replicated on ZGW

The Z/IP Gateway is reusing the script to parse SAPI logs. The script
was adjusted to be compatible with the ZGW logs. Adding a reference to
the ZGW copy on the original script.

Related-to: SiliconLabs/zipgateway#30

Author: lmolina

scripts/serial_decode_zpc.py

@@ -2,6 +2,9 @@
 # SPDX-License-Identifier: LicenseRef-MSLA
 # SPDX-FileCopyrightText: Silicon Laboratories Inc. https://www.silabs.com
 '''
+The script was replicated and updated to work with Z/IP Gateway
+See https://github.com/SiliconLabs/zipgateway/pull/30
+
 Created on 08/11/2011
 
 @author: aes