docs: update Mux Codes instructions for new UX

Author: ammario

docs/img/mux-codes-1.webp

@@ -13,10 +13,10 @@ Redemption is straightforward:
 1. Open Mux (see [install](/install) for instructions)
 1. Click the Settings icon in the top left corner (Cmd+, on macOS)
 1. Under Providers, enter the code under Mux Gateway:
-   ![Mux Gateway Code](./img/mux-gateway-code.webp)
-1. When sending a message or creating a workspace, select a `mux-gateway` model:
-   ![Mux Gateway Model](./img/mux-gateway-input.webp)
-   - Optionally, click Star to set the Mux Gateway model as your default model.
+   ![Mux Gateway Code](./img/mux-codes-1.webp)
+1. Under Models, ensure the Mux Gateway button is toggled for the model you want to use
+   ![Mux Gateway Model](./img/mux-codes-2.webp)
+   - Optionally, click Star to set the model as your default model.
 
 That's it! When you run out of credits, you can swap to a different code or
 begin using the model providers directly out-of-pocket.