Improve --local_rank arg comment (ultralytics#8409)

* add more docs

* add more docs

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update train.py

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

train.py

@@ -504,7 +504,7 @@ def parse_opt(known=False):
     parser.add_argument('--patience', type=int, default=100, help='EarlyStopping patience (epochs without improvement)')
     parser.add_argument('--freeze', nargs='+', type=int, default=[0], help='Freeze layers: backbone=10, first3=0 1 2')
     parser.add_argument('--save-period', type=int, default=-1, help='Save checkpoint every x epochs (disabled if < 1)')
-    parser.add_argument('--local_rank', type=int, default=-1, help='DDP parameter, do not modify')
+    parser.add_argument('--local_rank', type=int, default=-1, help='Automatic DDP Multi-GPU argument, do not modify')
 
     # Weights & Biases arguments
     parser.add_argument('--entity', default=None, help='W&B: Entity')