more gateweay docs

website/docs/developer/cloud/gateway.mdx

@@ -102,6 +102,17 @@ Otherwise, you can also work on the simulator device using the local host connec
 Device messages are pushed into the `messages` [Azure Storage Queue](https://learn.microsoft.com/en-us/azure/storage/queues/storage-queues-introduction) as a base-64 encoded JSON string.
 You can use any client library to access those messages.
 
+## GitHub Codespaces
+
+Running the local web server from [GitHub Codespaces](https://github.com/features/codespaces)
+allows you to run the Development Gateway in the cloud, which simplifies many connectivity issues with local networks.
+
+The Development Gateway can be run in a browser using [codesandbox.io](https://codesandbox.io/).
+
+-   go to https://github.com/microsoft/devicescript-gateway/ (or your forked repository)
+-   click the down arrow on **Code**
+-   click `create codespace on main`
+
 ## Codesandbox.io
 
 Running the local web server from [CodeSandbox.io](https://codesandbox.io/)
@@ -116,10 +127,15 @@ The Development Gateway can be run in a browser using [codesandbox.io](https://c
 ## MQTT
 
 The gateway can also be used as an MQTT server or a bridge to an existing MQTT server.
+You can configure a MQTT server by providing the `DEVS_MQTT_SERVER` environment variable.
 
 -   `publishMessage`, `subscribeMessage` from "@devicescript/cloud" will automatically be bridge to the MQTT server under the topic `devs/{deviceId}/(from|to)/{topic}`.
--   You can use the [MQTT Client](https://marketplace.visualstudio.com/items?itemName=kwkmp.mqttclient) in Visual Studio Code to connect to the MQTT server
-    and publish, subscribe to topics.
+-   You can override the `devs/.../from/...` routing scheme by starting your topic with `/`. For example, `/mytopic` will be routed to `mytopic`.
+
+::: tip
+You can use the [VSMqtt](https://marketplace.visualstudio.com/items?itemName=rpdswtk.vsmqtt) in Visual Studio Code to connect to the MQTT server
+and publish, subscribe to topics.
+:::
 
 ## Azure deployment (optional)