Adding a brief description of the API.

Author: peknis01

DOXYGEN_FRONTPAGE.md

@@ -1,11 +1,14 @@
-ARM mbed Client
+mbed Client API 
 ================
 
-## Introduction
-This is the Doxygen generated documentation of mbed Client.
-It should be used in conjunction with the [mbed Client Guide](https://docs.mbed.com/docs/mbed-client-guide/en/latest/)
+This is the Doxygen generated API documentation of mbed Client. See the [Files](files.html) section to find the documentation about specific API. It should be used together with the [mbed Client Guide](https://docs.mbed.com/docs/mbed-client-guide/en/latest/)
 hosted in http://docs.mbed.com.
 
-# API documentation
+The mbed Client high-level APIs allow mbed OS developers to create applications with LwM2M features as described in the [Lightweight Machine to Machine Technical Specification](http://technical.openmobilealliance.org/Technical/technical-information/release-program/current-releases/oma-lightweightm2m-v1-0):
+
+- Manage devices on mbed Device Server.
+- Securely communicate with internet services over the industry standard TLS/DTLS.
+- Fully control the endpoint and application logic.
+
+The API is written in C++ to allow quick application development.
 
-See [Files](files.html) section to find a documentation about specific API.