Add a Python tool to generate a PDF book from the repository documentation

[Anderson-Andre-P]

Hi @weeeBox,

I built a Python-based solution that converts this repository's Markdown documentation into a professionally formatted PDF book while preserving links, images, code blocks, and the overall document structure.

Since I didn't want to modify your repository directly, I published the implementation in my own repository:

https://github.com/Anderson-Andre-P/mobile-system-design

Hopefully it's useful to others as well.

book.pdf

[Anderson-Andre-P]

My idea was to make studying easier by creating a PDF that I can read on my smartphone or iPad. With a PDF, I can also highlight sections and add notes directly to the pages, which works much better for me.