Add example ttn test config file

iot/TTNTest/config.custom.h.example

@@ -0,0 +1,15 @@
+// Copy this file to have the name "config.custom.h", and fill in the 3 sections below
+
+// LoRaWAN NwkSKey, network session key
+// Big endian (i.e. msb)
+static const PROGMEM u1_t NWKSKEY[16] = { .... };
+
+// LoRaWAN AppSKey, application session key
+// Big endian (i.e. msb)
+static const u1_t PROGMEM APPSKEY[16] = { .... };
+
+// LoRaWAN end-device address (DevAddr)
+// See http://thethingsnetwork.org/wiki/AddressSpace
+// The library converts the address to network byte order as needed.
+// Big endian (i.e. msb)
+static const u4_t DEVADDR = 0x....; // <-- Change this address for every node!