[CI/Build] Add markdown linter (#11857)

Signed-off-by: Rafael Vasquez <rafvasq21@gmail.com>

docs/source/contributing/model/multimodal.md

@@ -200,6 +200,7 @@ def get_mm_max_tokens_per_item(self, seq_len: int) -> Mapping[str, int]:
 ```{note}
 Our [actual code](gh-file:vllm/model_executor/models/llava.py) is more abstracted to support vision encoders other than CLIP.
 ```
+
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@@ -248,6 +249,7 @@ def get_dummy_processor_inputs(
         mm_data=mm_data,
     )
 ```
+
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@@ -312,6 +314,7 @@ def _get_mm_fields_config(
 Our [actual code](gh-file:vllm/model_executor/models/llava.py) additionally supports
 pre-computed image embeddings, which can be passed to be model via the `image_embeds` argument.
 ```
+
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 ::::
 
@@ -369,6 +372,7 @@ def _get_prompt_replacements(
         ),
     ]
 ```
+
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