Add an index or table of contents

[MiguelAntonioRS]

With so many files, it’s hard to explore the content without manually searching.

Create an INDEX.md or update the README.md with a structured thematic index. Each entry should include:

Title or filename

Type (essay, theory, audio, summary)

Available format (.txt, .mhtml, etc.)

Consider linking each entry directly to the corresponding files.

This will greatly improve navigation and user experience.