Update README.md with usage instruction (#7)

Update README.md with usage instruction - Credits goes to eszkjc on Reddit

https://www.reddit.com/r/homeassistant/comments/eszkjc/zigbee_network_mapping_with_zha_my_77_node_network/

https://www.reddit.com/r/homeassistant/comments/eszkjc/zigbee_network_mapping_with_zha_my_77_node_network/

README.md

@@ -1,2 +1,24 @@
 # zha-map
 Build ZHA network topology map.
+
+[zha-map](https://github.com/zha-ng/zha-map) integration commponent for [Home Assistant](https://www.home-assistant.io) allow you to make a ZHA (Zigbee Home Automation) network topology map.
+
+Requires that you are already using the [ZHA](https://www.home-assistant.io/integrations/zha/) integration commponent in Home Assistant.
+
+Zigbee network mapping with zha-map can help you identify weak points like bad links between your devices.
+
+# Installation Instructions
+
+1. Install the zha_map custom component
+- https://github.com/zha-ng/zha-map
+2. Add zha_map: to your configuration.yaml and restart Home Assistant
+3. Wait for a scan to complete (logs to DEBUG, or use the new zha_map service to scan on demand)
+4. Install the zha-network-visualization-card lovelace card
+- https://github.com/dmulcahey/zha-network-visualization-card
+5. Add to your lovelace global config as type: module
+6. Add custom card (works best in panel mode): - type: 'custom:zha-network-visualization-card'
+
+# Usage
+The Zigbee coordinator will be represented by a rectangle at the top. Any device that serves as Zigbee router (usually all devices running on Mains electricity / grid power) will represented as ovals, and Zigbee end-device (usually battery powered sensors) will be represented by as circles.
+
+The lines between those representions show all the possible paths through Zigbee mesh. Any path with a LQI over 192 is shown as green, LQI 129-192 is shown as yellow, and anything 128 and lower is shown as red.