Fix MarkupLMProcessor option flag in MarkupLMProcessor documentation 
Author: davanstrien
Pull request: yes

# What does this PR do?

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Fixes a mistake in the docs for MarkupLMProcessor for use case 5. Currently the heading says `apply_ocr=False`, I believe this should be `parse_html=False`. 


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cc @NielsRogge @SaulLu @sgugger 


Comments:
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