doc(pan-cordio): Add documentation to README on how to enable Cordio LL

Author: Steve Cartmell

features/FEATURE_BLE/targets/TARGET_NORDIC/TARGET_NORDIC_CORDIO/TARGET_NRF5x/README.md

@@ -3,10 +3,14 @@
 To use this port amend your mbed_app.json file as following:
 ```json
         "NRF52840_DK": {
-            "target.features_add": ["BLE"]
+            "target.features_add": ["BLE"],
+            "target.extra_labels_add": ["CORDIO", "CORDIO_LL", "SOFTDEVICE_NONE", "NORDIC_CORDIO"],
+            "target.extra_labels_remove": ["SOFTDEVICE_COMMON", "SOFTDEVICE_S140_FULL", "NORDIC_SOFTDEVICE"]
         },
         "NRF52_DK": {
-            "target.features_add": ["BLE"]
+            "target.features_add": ["BLE"],
+            "target.extra_labels_add": ["CORDIO", "CORDIO_LL", "SOFTDEVICE_NONE", "NORDIC_CORDIO"],
+            "target.extra_labels_remove": ["SOFTDEVICE_COMMON", "SOFTDEVICE_S132_FULL", "NORDIC_SOFTDEVICE"]
         }
 ```