Add OpenHAB3 tutorial and BLE binary (#1254)

* Add OpenHAB3 tutorial and BLE binary

* Small text changes

Just a few small text changes, also writing out OMG as OpenMQTTGateway, probably clearer for new to OMG users.

Co-authored-by: DigiH <github@digih.net>

docs/.vuepress/config.js

@@ -95,6 +95,7 @@ module.exports = {
           sidebarDepth: 1,    // optional, defaults to 1
           children: [
             'integrate/openhab2',
+            'integrate/openhab3',
             'integrate/home_assistant',
             'integrate/node_red',
             'integrate/aws_iot'