Update prompts/titles_and_thumbnails.txt

prompts/titles_and_thumbnails.txt

@@ -13,6 +13,8 @@ Thumbnail: 2-4 ALL CAPS words that amplify the intrigue
 - Create intellectual curiosity without sensationalism
 - Make the viewer wonder "What's the story here?"
 
+**Important: Generate the response as plain text only. Do not use any Markdown formatting (no '#', '*', '_', list formatting, bolding, etc.).**
+
 Here are examples of successful title-thumbnail combinations from previous episodes:
 {title_examples}