[Docs] Make sure important decode and generate method are nicely disp…

…layed in Whisper docs (#26927)

better docstrings whisper

docs/source/en/model_doc/whisper.md

@@ -48,6 +48,8 @@ The original code can be found [here](https://github.com/openai/whisper).
  - get_special_tokens_mask
  - create_token_type_ids_from_sequences
  - save_vocabulary
+ - batch_decode
+ - decode
 
 ## WhisperTokenizerFast
 
@@ -57,6 +59,8 @@ The original code can be found [here](https://github.com/openai/whisper).
  - get_special_tokens_mask
  - create_token_type_ids_from_sequences
  - save_vocabulary
+ - batch_decode
+ - decode
 
 ## WhisperFeatureExtractor
 
@@ -82,6 +86,7 @@ The original code can be found [here](https://github.com/openai/whisper).
 
 [[autodoc]] WhisperForConditionalGeneration
  - forward
+ - generate
 
 ## WhisperForAudioClassification