Add PON mode configuration instructions

Add instructions for setting PON mode with GPON, EPON, and Ethernet options.

Author: lmepisowifi

_ont/ont-yotc-m2-2050-g40.md

@@ -194,6 +194,21 @@ mib set ELAN_MAC_ADDR 1A2B3C4D5E6F
 ```
 mib set LAN_IP_ADDR 192.168.8.1
 ```
+## Switch PON Mode
+```
+# GPON mode
+mib set PON_MODE 1
+```
+
+```
+# EPON mode
+mib set PON_MODE 2
+```
+
+```
+# Ethernet mode
+mib set PON_MODE 3
+```
 
 ## Checking the currently active image
 ```