Update config.py.example

Add configurable settings for QOS and retain flag.

src/config.py.example

@@ -35,4 +35,10 @@ memory = True
 uptime = True
 # Enable wifi_signal for unit of measuring % or wifi_signal_dbm for unit of meaning dBm
 wifi_signal = True
-wifi_signal_dbm = False
+wifi_signal_dbm = False
+
+# Retain flag for published topics
+retain = True
+
+# QOS setting for published topics: 0,1,2 are acceptable values
+qos = 0