Add: Act as a Book Summarizer

[riakashyap]

Added a new prompt that summarizes the key ideas from a book.

Whether it’s a self-help book, an educational text, or any other genre, the prompt captures the most important points, allowing readers to quickly get the main takeaways without having to read the entire book.

• [✓ ] I've confirmed the prompt works well
• [✓ ] I've added Contributed by: [@yourusername](https://github.com/yourusername)
• [✓ ] I've added to the README.md
• [ ✓] I've added to the prompts.csv
  • [✓ ] Escaped quotes by double-quoting them
  • [✓ ] No spaces after commas after double quotes. e.g. "Hello","hi", not "Hello", "hi"
  • [ ✓] Removed "Act as" from the title on CSV

Please make sure you've completed all the checklist.