Update README.md (#16)

* Update README.md

* fix problem with mbed tools config behaviour

Author: paul-szczepanek-arm

README.md

@@ -1,3 +1,41 @@
 # Experimental services for Mbed OS BLE
 
 This repository is an incubator for standard and common Bluetooth services development.
+
+## Contents
+
+The repo contains multiple BLE services designed to work with Mbed OS. They are not officially supported and are not
+part of Mbed OS itself. This is a community led effort and we welcome all contributions, which should follow the
+decisions published in the `doc/adr` directory.
+
+Services are are in the `services` directory. Each BLE service is an Mbed OS library. The name of each library
+is in the `mbed_lib.json` file inside each of the service directories. They follow the pattern `ble-service-name`. 
+
+## How to use a service
+
+Inside your Mbed OS project, include a file called 'mbed-os-experimental-ble-services.lib' with contents:
+
+```
+https://github.com/ARMmbed/mbed-os-experimental-ble-services
+```
+
+Call `mbed deploy`. This will check out this repository into your project.
+
+To use a particular service you will need to now add the library that contains it into your application.
+
+Inside your `mbed_app.json` you need to override the `requires` section for your platform.
+Add the name of the library containing the service.
+
+For example, if you want to use the DFU service, add this to your `mbed_app.json`: 
+
+```
+    "target_overrides": {
+        "*": {
+            "target.requires": [ "ble-service-DFU" ]
+        },
+    }
+```
+
+### License and contributions
+
+The software is provided under Apache-2.0 license. Contributions to this project are accepted under the same license.