[Doc]: fix wrong imaeg linked on line 93 (#9054)

Author: akshaygulabrao

docs/en/get_started.md

@@ -93,7 +93,7 @@ from mmdet.apis import init_detector, inference_detector
 config_file = 'yolov3_mobilenetv2_320_300e_coco.py'
 checkpoint_file = 'yolov3_mobilenetv2_320_300e_coco_20210719_215349-d18dff72.pth'
 model = init_detector(config_file, checkpoint_file, device='cpu')  # or device='cuda:0'
-inference_detector(model, 'demo/cat.jpg')
+inference_detector(model, 'demo/demo.jpg')
 ```
 
 You will see a list of arrays printed, indicating the detected bounding boxes.