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