Update tradfri docs

source/_components/tradfri.markdown

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+---
+layout: page
+title: "IKEA Trådfri (Tradfri)"
+description: "Access and control your ZigBee-based IKEA Trådfri (Tradfri) devices."
+date: 2017-04-12 22.04
+sidebar: true
+featured: true
+comments: false
+sharing: true
+footer: true
+logo: ikea.svg
+ha_category: Light
+ha_iot_class: "Local Polling"
+ha_release: 0.43
+---
+
+Support for the IKEA Trådfri (Tradfri) gateway. The gateway can control lights connected to it.
+
+NB: for this to work, you need to install a modified lib-coap library:
+
+```bash
+apt-get install libtool
+
+git clone --depth 1 --recursive -b dtls https://github.com/home-assistant/libcoap.git
+cd libcoap
+./autogen.sh
+./configure --disable-documentation --disable-shared --without-debug CFLAGS="-D COAP_DEBUG_FD=stderr"
+make
+make install
+```
+
+To enable these lights, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+tradfri:
+  host: 192.168.0.129
+  api_key: <on back of gateway>
+```