[LongT5] Correct docs long t5 (#18669)

* add first generation tutorial

* [LongT5 Docs] Correct docs

* correct expected string

* remove incorrect file

src/transformers/models/longt5/modeling_longt5.py

@@ -1966,13 +1966,12 @@ class LongT5ForConditionalGeneration(LongT5PreTrainedModel):
         ... )
 
         >>> # Let's try a very long input.
-        >>> input_ids = tokenizer(
-        ...     "summarize: " + 100 * "studies have shown that owning a dog is good for you ", return_tensors="pt"
-        ... ).input_ids  # Batch size 1
+        >>> inputs = tokenizer(100 * "studies have shown that owning a dog is good for you ", return_tensors="pt")
+        >>> input_ids = inputs.input_ids
 
         >>> outputs = model.generate(input_ids)
         >>> print(tokenizer.decode(outputs[0], skip_special_tokens=True))
-        abstractthe aim of this article is to summarize the studies have shown that owning a dog
+        abstractthe aim of this article is to provide an overview of the literature on the role of dog
         ```"""
         use_cache = use_cache if use_cache is not None else self.config.use_cache
         return_dict = return_dict if return_dict is not None else self.config.use_return_dict