Added default MCU temperature for sensors

examples/simple_sensor/SensorMesh.cpp

@@ -182,6 +182,12 @@ uint8_t SensorMesh::handleRequest(uint8_t perms, uint32_t sender_timestamp, uint
     sensors.querySensors(0xFF & perm_mask, telemetry);  // allow all telemetry permissions for admin or guest
     // TODO: let requester know permissions they have:  telemetry.addPresence(TELEM_CHANNEL_SELF, perms);
 
+    // This default temperature will be overridden by external sensors (if any)
+    float temperature = board.getMCUTemperature();
+    if (!isnan(temperature)) { // Supported boards with built-in temperature sensor. ESP32-C3 may return NAN
+      telemetry.addTemperature(TELEM_CHANNEL_SELF, temperature); // Built-in MCU Temperature
+    }
+
     uint8_t tlen = telemetry.getSize();
     memcpy(&reply_data[4], telemetry.getBuffer(), tlen);
     return 4 + tlen;  // reply_len