Add README with some settings.

Signed-off-by: Marcus Edel <marcus.edel@collabora.com>

Author: zoq

demo/football/README.md

@@ -3,8 +3,12 @@
 Real-time football broadcast overlay: **detection → tracking → overlay**
 (`pyml_yolo`/`pyml_objectdetector` -> `pyml_tracker` -> `pyml_football_overlay`).
 
-The overlay draws a foot ellipse per subject (players one colour, referee gold),
-a green triangle on the ball, motion trails, and a focal-player HUD + ball contacts + distance.
+The overlay draws a foot ellipse per player coloured by team (red/blue, voted
+from jersey hue), a gold ellipse for referees, motion trails (off by default),
+and a focal-player HUD with headshot, ball contacts, and distance travelled.
+Players whose team isn't decided yet (and unclassifiable kits, e.g. the
+goalkeeper) are left unmarked rather than drawn in a placeholder colour. The
+ball is tracked for contact counting but its marker is off by default.
 
 ## Run
 
@@ -13,6 +17,25 @@ a green triangle on the ball, motion trails, and a focal-player HUD + ball conta
 demo/football/run.sh
 demo/football/run.sh 08fd33_4.mp4 demo/football/out.mp4 1280x720
 
+# file -> live on-screen
+demo/football/run.sh display
+demo/football/run.sh display 08fd33_4.mp4 1280x720
+
 # live camera -> on-screen
 demo/football/run.sh camera /dev/video0
 ```
+
+## Environment knobs
+
+| Var        | Default | Meaning |
+|------------|---------|---------|
+| `BACKEND`  | `pt`    | `pt` = PyTorch `pyml_yolo`; `fp16` = ONNX FP16 via `pyml_objectdetector` (CUDA). |
+| `INTERVAL` | `3`     | Run detection every Nth frame; the tracker/overlay still update every frame, so it stays smooth at ~N× less inference cost. The main real-time lever. |
+
+```bash
+BACKEND=fp16 demo/football/run.sh display     # faster inference path
+INTERVAL=5   demo/football/run.sh display     # detect every 5th frame
+INTERVAL=1   demo/football/run.sh             # detect every frame (max accuracy)
+```
+
+