Return metrics, Update docs (#846)

README.md

@@ -98,8 +98,8 @@ model = YOLO("yolov8n.yaml")  # build a new model from scratch
 model = YOLO("yolov8n.pt")  # load a pretrained model (recommended for training)
 
 # Use the model
-results = model.train(data="coco128.yaml", epochs=3)  # train the model
-results = model.val()  # evaluate model performance on the validation set
+model.train(data="coco128.yaml", epochs=3)  # train the model
+metrics = model.val()  # evaluate model performance on the validation set
 results = model("https://ultralytics.com/images/bus.jpg")  # predict on an image
 success = model.export(format="onnx")  # export the model to ONNX format
 ```