Create README.md

Signed-off-by: David Rotermund <54365609+davrot@users.noreply.github.com>

cv2/webcam/README.md

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+# Read from Webcam
+{:.no_toc}
+
+<nav markdown="1" class="toc-class">
+* TOC
+{:toc}
+</nav>
+
+## The goal
+
+We want to capture the webcam via CV2.
+
+Questions to [David Rotermund](mailto:davrot@uni-bremen.de)
+
+```shell
+pip install opencv-contrib-python
+```
+
+```python
+import numpy as np
+import cv2
+
+def record_video(
+    camera_index: int,
+    n_frames: int,
+    fps: float = 20.0,
+    framesize: tuple[int, int] = (640, 480),
+    display: bool = False,
+) -> tuple[bool, np.ndarray]:
+    cap = cv2.VideoCapture(camera_index)
+    assert cap.isOpened() is True, "record_video: Errror during opening the device!"
+
+    cap.set(cv2.CAP_PROP_FPS, fps)
+    cap.set(cv2.CAP_PROP_FRAME_WIDTH, framesize[0])
+    cap.set(cv2.CAP_PROP_FRAME_HEIGHT, framesize[1])
+    print(
+        f"Capturing: {cap.get(cv2.CAP_PROP_FRAME_WIDTH):.0f} x {cap.get(cv2.CAP_PROP_FRAME_HEIGHT):.0f} @ {cap.get(cv2.CAP_PROP_FPS):.1f}."
+    )
+
+    for i_frame in range(n_frames):
+        success, frame = cap.read()
+        assert success is True, "record_video: Some error during capturing occurred!"
+
+        if i_frame == 0:
+            frames = np.zeros((*frame.shape, n_frames)).astype(np.uint8)
+        frames[:, :, :, i_frame] = frame
+        if display is True:
+            cv2.imshow("Capture", frame)
+            retval = cv2.waitKey(1)
+            if retval != -1:
+                frames = frames[:, :, :, 0 : i_frame + 1]
+                break
+    cap.release()
+    if display is True:
+        cv2.destroyWindow("Capture")
+    return success, frames
+
+
+if __name__ == "__main__":
+    success, frames = record_video(
+        camera_index=0,
+        n_frames=200,
+        fps=20.0,
+        framesize=(640, 480),
+        display=True,
+    )
+
+    print(success) # -> True
+    print(frames.shape) # -> (480, 640, 3, 200)
+```