fix: correct YouTube capitalization in README

Good day,

I noticed 'Youtube URLs' should be 'YouTube URLs' to match the official brand capitalization.

Thank you for your work on this project. I hope this small fix is helpful. Please let me know if there's anything to adjust.

Warmly, RoomWithOutRoof

Author: RoomWithOutRoof

README.md

@@ -26,7 +26,7 @@ MarkItDown currently supports the conversion from:
 - HTML
 - Text-based formats (CSV, JSON, XML)
 - ZIP files (iterates over contents)
-- Youtube URLs
+- YouTube URLs
 - EPubs
 - ... and more!