[scripts.train] Improve documentation

src/ptbench/scripts/train.py

@@ -170,8 +170,9 @@ def reusable_options(f):
         "-P",
         help="""Use multiprocessing for data loading: if set to -1 (default),
         disables multiprocessing data loading.  Set to 0 to enable as many data
-        loading instances as processing cores as available in the system.  Set to
-        >= 1 to enable that many multiprocessing instances for data loading.""",
+        loading instances as processing cores available in the system.  Set to
+        >= 1 to enable that many multiprocessing instances for data
+        loading.""",
         type=click.IntRange(min=-1),
         show_default=True,
         required=True,