mbed_app.json configured to operate on senet

To enable cayenne, edit mbed_app.json, assign pins for desired function

Example:

        "cayenne": {
            "help": "compile main_cayenne.cpp instead of main.cpp",
            "value": 1
        },
        "analog_in_pin": {
            "help": "PA_0, PA_4, PA_5",
            "value": "PA_0"
        },
        "analog_out_pin": {
            "help": "PA_0, PB_5, PB_10, PB_11",
            "value": "PB_11"
        },
        "_digital_out_pin": {
            "help": "",
            "value": ""
        }
Revision:
46:a124538e2891
Parent:
26:f07f5febf97f
Child:
52:1bd775571014
--- a/README.md	Thu Jan 03 15:30:32 2019 +0000
+++ b/README.md	Thu Jan 10 12:15:30 2019 +0000
@@ -25,7 +25,7 @@
 
 If you are using an Mbed Enabled radio shield such as [Mbed SX1276 shield LoRa](https://os.mbed.com/components/SX1276MB1xAS/) or [Mbed SX1272 LoRa shield ](https://os.mbed.com/components/SX1272MB2xAS/) with any Mbed Enabled board, this part is relevant. You can use any Mbed Enabled board that comes with an arduino form factor.
 
-Please select your radio type by modifying the `lora-radio` field and providing a pin set if it is different from the default. For example:
+Please select your radio type by modifying the `lora-radio` field in `mbed_app.json` and providing a pin set if it is different from the default. For example:
 
 ```json
 "lora-radio": {