Fix typo on the getting started section of `README.md`

After re-bootrapping the project, I realised that the README had some typo that I fixed in this commit.

README.md

@@ -73,22 +73,28 @@ For more installation guideline, check out our installation guide here: https://
 
 1. Install the example python dependencies:
 ```bash
-pip install opencv-python numpy pyarrow
+pip install -r https://raw.githubusercontent.com/dora-rs/dora/v0.2.4/examples/python-operator-dataflow/requirements.txt
 ```
 
 2. Get some example operators:
 ```bash
-wget https://raw.githubusercontent.com/dora-rs/dora/main/examples/python-operator-dataflow/webcam.py
-wget https://raw.githubusercontent.com/dora-rs/dora/main/examples/python-operator-dataflow/plot.py
-wget https://raw.githubusercontent.com/dora-rs/dora/main/examples/python-operator-dataflow/utils.py
-wget https://raw.githubusercontent.com/dora-rs/dora/main/examples/python-operator-dataflow/dataflow.yml
+wget https://raw.githubusercontent.com/dora-rs/dora/v0.2,4/examples/python-operator-dataflow/webcam.py
+wget https://raw.githubusercontent.com/dora-rs/dora/v0.2.4/examples/python-operator-dataflow/plot.py
+wget https://raw.githubusercontent.com/dora-rs/dora/v0.2.4/examples/python-operator-dataflow/utils.py
+wget https://raw.githubusercontent.com/dora-rs/dora/v0.2.4/examples/python-operator-dataflow/object_detection.py
+wget https://raw.githubusercontent.com/dora-rs/dora/v0.2.4/examples/python-operator-dataflow/dataflow.yml
 ```
 
 3. Start the dataflow
 ```bash
-dora start dataflow.yaml --attach --hot-reload
+dora up
+dora start dataflow.yml --attach --hot-reload
 ```
 
+> Make sure to have a webcam 
+
+To stop your dataflow, you can use <kbd>ctrl</kbd>+<kbd>c</kbd>
+
 To go further, you can add a yolov5 operator, check out our getting started here: https://dora.carsmos.ai/docs/guides/getting-started/yolov5
 
 ## Documentation

examples/python-operator-dataflow/webcam.py

@@ -4,13 +4,18 @@
 import time
 from typing import Callable
 
+import os
 import cv2
+import numpy as np
 import pyarrow as pa
 
 from dora import DoraStatus
 
 CAMERA_WIDTH = 640
 CAMERA_HEIGHT = 480
+CAMERA_INDEX = os.getenv("CAMERA_INDEX", 0)
+
+font = cv2.FONT_HERSHEY_SIMPLEX
 
 
 class Operator:
@@ -19,7 +24,7 @@ class Operator:
     """
 
     def __init__(self):
-        self.video_capture = cv2.VideoCapture(0)
+        self.video_capture = cv2.VideoCapture(CAMERA_INDEX)
         self.start_time = time.time()
         self.video_capture.set(cv2.CAP_PROP_FRAME_WIDTH, CAMERA_WIDTH)
         self.video_capture.set(cv2.CAP_PROP_FRAME_HEIGHT, CAMERA_HEIGHT)
@@ -32,13 +37,28 @@ class Operator:
         match dora_event["type"]:
             case "INPUT":
                 ret, frame = self.video_capture.read()
-                frame = cv2.resize(frame, (CAMERA_WIDTH, CAMERA_HEIGHT))
                 if ret:
-                    send_output(
-                        "image",
-                        pa.array(frame.ravel()),
-                        dora_event["metadata"],
+                    frame = cv2.resize(frame, (CAMERA_WIDTH, CAMERA_HEIGHT))
+
+                ## Push an error image in case the camera is not available.
+                else:
+                    frame = np.zeros((CAMERA_HEIGHT, CAMERA_WIDTH, 3), dtype=np.uint8)
+                    cv2.putText(
+                        frame,
+                        "No Webcam was found at index %d" % (CAMERA_INDEX),
+                        (int(30), int(30)),
+                        font,
+                        0.75,
+                        (255, 255, 255),
+                        2,
+                        1,
                     )
+
+                send_output(
+                    "image",
+                    pa.array(frame.ravel()),
+                    dora_event["metadata"],
+                )
             case "STOP":
                 print("received stop")
             case other: