docs(jetson): Clarify Jetson Nano 16GB image for desktop preview

Updates the README.md to specify "prebuilt" when referring to the Jetson Nano 16GB image.
This provides clearer context for applying the `gtk_gtksink_patch_installer.sh` to restore `gtksink` preview support on NVIDIA Jetson devices.

[auto-enhanced]

Author: steveseguin

README.md

@@ -176,7 +176,7 @@ cd ~/raspberry_ninja/installers/nvidia_jetson
 ./quick_update.sh
 ```
 
-If you plan to launch the desktop preview from GNOME (for example when running `publish.py` from a terminal window in the GUI) on the Jetson Nano 16GB image, run the Gtk/GStreamer patch helper once to restore the `gtksink` preview support:
+If you plan to launch the desktop preview from GNOME (for example when running `publish.py` from a terminal window in the GUI) on the prebuilt Jetson Nano 16GB image, run the Gtk/GStreamer patch helper once to restore the `gtksink` preview support:
 
 ```
 cd ~/raspberry_ninja/installers/nvidia_jetson