Add readme

Author: Seppo Takalo

README.md

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+# Example Mesh application for mbed OS
+
+This applications tries to be the simplest one that utilizes our Mesh networking stack.
+
+Basically only thing it does, is to join unsecure *6LoWPAN-ND* network.
+
+See file `mbed_app.json` for example how to define IEEE 802.15.4 channel to use.
+
+## Changing the radio driver
+
+In order to run 6LoWPAN-ND network, you need working RF driver for Nanostack.
+
+Provided example uses Atmel AT86RF233. To replace that do
+```
+mbed remove atmel-rf-driver
+```
+
+and then
+```
+mbed add <your RF driver address>
+```
+
+And then just `mbed compile`