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

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

docs/source/serving/multimodal_inputs.md

@@ -303,6 +303,7 @@ vllm serve llava-hf/llava-onevision-qwen2-0.5b-ov-hf --task generate --max-model
 ```
 
 Then, you can use the OpenAI client as follows:
+
 ```python
 from openai import OpenAI