Fix header level (#21072)

fix header level

docs/source/en/pipeline_tutorial.mdx

@@ -213,7 +213,7 @@ Specify your task and pass your image to the classifier. The image can be a link
 [{'score': 0.4335, 'label': 'lynx, catamount'}, {'score': 0.0348, 'label': 'cougar, puma, catamount, mountain lion, painter, panther, Felis concolor'}, {'score': 0.0324, 'label': 'snow leopard, ounce, Panthera uncia'}, {'score': 0.0239, 'label': 'Egyptian cat'}, {'score': 0.0229, 'label': 'tiger cat'}]
 ```
 
-### Text pipeline
+## Text pipeline
 
 Using a [`pipeline`] for NLP tasks is practically identical.
 
@@ -230,7 +230,7 @@ Using a [`pipeline`] for NLP tasks is practically identical.
 {'sequence': 'I have a problem with my iphone that needs to be resolved asap!!', 'labels': ['urgent', 'phone', 'computer', 'not urgent', 'tablet'], 'scores': [0.504, 0.479, 0.013, 0.003, 0.002]}
 ```
 
-### Multimodal pipeline
+## Multimodal pipeline
 
 The [`pipeline`] supports more than one modality. For example, a visual question answering (VQA) task combines text and image. Feel free to use any image link you like and a question you want to ask about the image. The image can be a URL or a local path to the image.