Make clearer about zero_init requirements (#29879)

* Docstring to note about zero init

* Check for accelerate

* Change conditional return

* Tweak

* Add new accelerate-specific zero3 check

* Fix import

* Revert to RTFM

* Update src/transformers/modeling_utils.py
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

---------
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

src/transformers/training_args.py

@@ -504,6 +504,11 @@ class TrainingArguments:
             evolve in the future. The value is either the location of DeepSpeed json config file (e.g.,
             `ds_config.json`) or an already loaded json file as a `dict`"
 
+            <Tip warning={true}>
+                If enabling any Zero-init, make sure that your model is not initialized until
+                *after* initializing the `TrainingArguments`, else it will not be applied.
+            </Tip>
+
         accelerator_config (`str`, `dict`, or `AcceleratorConfig`, *optional*):
             Config to be used with the internal `Accelerator` implementation. The value is either a location of
             accelerator json config file (e.g., `accelerator_config.json`), an already loaded json file as `dict`,