Add "#!/usr/bin/python" to the top of overlay examples

This means they can run directly without having to invoke the Python
interpreter explicitly (like the other examples).

Signed-off-by: David Plowman <[email protected]>

Author: davidplowman

examples/overlay_drm.py

@@ -1,3 +1,5 @@
+#!/usr/bin/python3
+
 from picamera2.picamera2 import *
 import numpy as np
 import time

examples/overlay_gl.py

@@ -1,3 +1,5 @@
+#!/usr/bin/python3
+
 from picamera2.picamera2 import *
 import numpy as np
 import time

examples/overlay_null.py

@@ -1,3 +1,5 @@
+#!/usr/bin/python3
+
 from picamera2.picamera2 import *
 import numpy as np
 import time

examples/overlay_qt.py

@@ -1,3 +1,5 @@
+#!/usr/bin/python3
+
 from picamera2.picamera2 import *
 import numpy as np
 import time