Update links to https://docs.ultralytics.com (#11412)

* Update links

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segment/train.py

@@ -12,7 +12,7 @@ Usage - Multi-GPU DDP training:
 
 Models:     https://github.com/ultralytics/yolov5/tree/master/models
 Datasets:   https://github.com/ultralytics/yolov5/tree/master/data
-Tutorial:   https://github.com/ultralytics/yolov5/wiki/Train-Custom-Data
+Tutorial:   https://docs.ultralytics.com/yolov5/tutorials/train_custom_data
 """
 
 import argparse
@@ -167,8 +167,10 @@ def train(hyp, opt, device, callbacks):  # hyp is path/to/hyp.yaml or hyp dictio
 
     # DP mode
     if cuda and RANK == -1 and torch.cuda.device_count() > 1:
-        LOGGER.warning('WARNING ⚠️ DP not recommended, use torch.distributed.run for best DDP Multi-GPU results.\n'
-                       'See Multi-GPU Tutorial at https://github.com/ultralytics/yolov5/issues/475 to get started.')
+        LOGGER.warning(
+            'WARNING ⚠️ DP not recommended, use torch.distributed.run for best DDP Multi-GPU results.\n'
+            'See Multi-GPU Tutorial at https://docs.ultralytics.com/yolov5/tutorials/multi_gpu_training to get started.'
+        )
         model = torch.nn.DataParallel(model)
 
     # SyncBatchNorm