Mention why one needs to specify max_steps in Trainer (#22333)

* Mention why one needs to specify max_steps in Trainer

* dummy change to trigger CI

src/transformers/trainer.py

@@ -544,7 +544,10 @@ class Trainer:
             logger.info("max_steps is given, it will override any value given in num_train_epochs")
 
         if train_dataset is not None and not has_length(train_dataset) and args.max_steps <= 0:
-            raise ValueError("train_dataset does not implement __len__, max_steps has to be specified")
+            raise ValueError(
+                "The train_dataset does not implement __len__, max_steps has to be specified. "
+                "The number of steps needs to be known in advance for the learning rate scheduler."
+            )
 
         if (
             train_dataset is not None