Update documentation suggestion in top level readme (#23978)

docs/contributing.md

@@ -105,7 +105,9 @@ enum my_keycodes {
 
 Before opening a pull request, you can preview your changes if you have set up the development environment by running this command from the `qmk_firmware/` folder:
 
-    qmk docs
+```
+qmk docs
+```
 
 and navigating to `http://localhost:5173/`.