[RWKV] Add note in doc on RwkvStoppingCriteria (#25055)

* Add note in doc on `RwkvStoppingCriteria`

* give some breathing space to the code

docs/source/en/model_doc/rwkv.md

@@ -51,6 +51,24 @@ output_two = outputs.last_hidden_state
 torch.allclose(torch.cat([output_one, output_two], dim=1), output_whole, atol=1e-5)
 ```
 
+If you want to make sure the model stops generating when `'\n\n'` is detected, we recommend using the following stopping criteria:
+
+```python 
+from transformers import StoppingCriteria
+
+class RwkvStoppingCriteria(StoppingCriteria):
+    def __init__(self, eos_sequence = [187,187], eos_token_id = 537):
+        self.eos_sequence = eos_sequence
+        self.eos_token_id = eos_token_id
+
+    def __call__(self, input_ids: torch.LongTensor, scores: torch.FloatTensor, **kwargs) -> bool:
+        last_2_ids = input_ids[:,-2:].tolist()
+        return self.eos_sequence in last_2_ids
+
+
+output = model.generate(inputs["input_ids"], max_new_tokens=64, stopping_criteria = [RwkvStoppingCriteria()])
+```
+
 ## RwkvConfig
 
 [[autodoc]] RwkvConfig