Update README (#2002)

Restructure and add chapter about Wi-SUN

Author: Arto Kinnunen

README.md

@@ -1,17 +1,39 @@
-ARM IPV6/6LoWPAN stack.
+ARM Mesh networking stack
 =======================
 
-This repository contains the ARM IPv6/6LoWPAN/Thread Stack for mbed OS.
+This repository contains the ARM mesh networking stack that  provides support for the following mesh protocols:
+
+  * 6LoWPAN with Neighbor Discovery (ND) and Mesh Link Establishment (MLE)
+  * Thread
+  * Wi-SUN
+ 
+ All networking stacks are using IEEE 802.15.4 based radios.
+  
+The full documentation is hosted in [Mbed OS documentation](https://os.mbed.com/docs/mbed-os/latest/reference/mesh-tech.html).
+
+On mbed OS, mesh networking stacks can be used  through [Mbed Mesh API](https://os.mbed.com/docs/mbed-os/latest/apis/mesh-api.html) and [Network Socket API](https://os.mbed.com/docs/mbed-os/v5.11/apis/network-socket.html).
+
+To see, how the mesh networking stack works, check the example application [mbed-os-example-mesh-minimal](https://github.com/ARMmbed/mbed-os-example-mesh-minimal).
+
+  
+##6LoWPAN with ND and MLE
+
+This networking stack is using standard 6LoWPAN and uses:
+
+* Neighbor Discovery Protocol ([RFC4861](https://tools.ietf.org/html/rfc4861)) to locate other devices in the mesh network. 
+* Mesh-Link-Establishment ([draft-kelsey-intarea-mesh-link-establishment-06](https://tools.ietf.org/html/draft-kelsey-intarea-mesh-link-establishment-06)) is used for establishing and configuring secure radio links. 
+  
+##Thread
+Thread is standardized by [Thread group](https://www.threadgroup.org/).
 
 ![](docs/img/thread_certified.png)
 
 mbed OS is now a Thread Certified Component. Using IPv6 with 6LoWPAN as the foundation, Thread technology provides a low-power, self-healing mesh network designed for the home.
 
-The documentation is hosted in [here](https://os.mbed.com/docs/v5.6/tutorials/6lowpan-mesh.html).
-
-On mbed OS, usage is through [mbed Mesh API](https://os.mbed.com/docs/v5.6/reference/mesh.html) and [Socket API](https://os.mbed.com/docs/v5.6/reference/network-socket.html).
+##Wi-SUN
+Wi-SUN (Smart Utility Networks) specification is standardized by [Wi-SUN Alliance](https://www.wi-sun.org/). 
 
-To see, how the 6LoWPAN Stack works, check the example application [mbed-os-example-mesh-minimal](https://github.com/ARMmbed/mbed-os-example-mesh-minimal).
+Mbed OS release 5.12 contains the initial Mbed Wi-SUN FAN implementation. Functionality of the Mbed Wi-SUN network stack will be updated when the Wi-SUN protocol is specified further.
 
 ## License