feat: add author add-book feature and list feature (develop)

[peepsbruh]

This PR adds a simple text-file prototype of the "add book" feature and the "list all books" feature for the book app.

Files added:

• athul_pp_book_app/add_books_feature/create_book.txt

  • "This is the feature for the author to add a new book."

• athul_pp_book_app/add_books_feature/list_all_books.txt

  • "This is the feature which shows the user all the books they’ve created as a list."
  • "List all books will list all books in ascending order."

Branching & commits:

• create_book.txt was added on develop.
• list_all_books.txt was added and updated on feature, then merged into develop.

Please review and merge into main. Thanks!