More explicit help how to cycle the cameras (#6162)

# Objective

Scene viewer example has switch camera keys defined, but only one camera was instantiated on the scene.

## Solution

More explicit help how to cycle the cameras, explaining that more cameras must be present in loaded scene.





Co-authored-by: Fanda Vacek <fvacek@elektroline.cz>

examples/tools/scene_viewer.rs

@@ -31,7 +31,7 @@ Controls:
     Q           - down
     L           - animate light direction
     U           - toggle shadows
-    C           - cycle through cameras
+    C           - cycle through the camera controller and any cameras loaded from the scene
     5/6         - decrease/increase shadow projection width
     7/8         - decrease/increase shadow projection height
     9/0         - decrease/increase shadow projection near/far