Add --retro-logo flag to the README

README.md

@@ -74,6 +74,19 @@ Support for existing JupyterLab themes!
 
 ![themes](https://user-images.githubusercontent.com/591645/101953333-75d9c180-3bfa-11eb-868f-af54d1ea7091.gif)
 
+For an even more retro look, you might want to start `retrolab` with the `--retro-logo` CLI flag:
+
+```bash
+jupyter retro --retro-logo
+
+# or
+# jupyter retro --RetroApp.retro_logo=True
+```
+
+Example with the [JupyterLab Miami Nights Theme](https://github.com/timkpaine/jupyterlab_miami_nights) installed as a prebuilt extension:
+
+![image](https://user-images.githubusercontent.com/591645/119634905-77e3b580-be13-11eb-9c4c-d187ebea9df8.png)
+
 ### Zen Mode 😌
 
 ![compact-zen-mode](https://user-images.githubusercontent.com/591645/101923740-149cf880-3bd0-11eb-9617-e3349a76d034.gif)