Add yolov5 python file

Signed-off-by: shiyu22 <shiyu.chen@zilliz.com>

__init__.py

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+from yolov5.yolov5 import Yolov5
+
+
+def yolov5():
+    return Yolov5()

requirements.txt

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+matplotlib>=3.2.2
+opencv-python>=4.1.2
+torch>=1.7.0
+torchvision>=0.8.1
+seaborn

yolov5.py

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+import torch
+import numpy
+from towhee.operator import NNOperator
+
+@register(outputschema=['boxes', 'classes', 'scores'])
+class Yolov5(NNOperator):
+    def __init__(self, model_name):
+        super().__init__()
+        self._model = torch.hub.load("ultralytics/yolov5", model_name, pretrained=True)
+
+    def __call__(self, img: numpy.ndarray):
+        # Get object detection results with YOLOv5 model
+        results = self._model(img)
+        
+        boxes = results.xyxy[0]
+        classes = list(results.pandas().xyxy[0].name)
+        scores = list(results.pandas().xyxy[0].confidence)
+        return boxes, classes, scores