Fix broken PyBoy link in resources.md (#77)

Updates the link for the PyBoy document to a working link.

website/resources.md

@@ -165,7 +165,7 @@ This project is open source and community-lead. Come <a href="https://gbdev.io/c
 ## Emulator Development
 
 - [Reverse Engineering fine details of Game Boy hardware](https://www.youtube.com/watch?v=GBYwjch6oEE) - 43 minutes talk by Gekkio given at Disobey 2018 ([errata](https://gekkio.fi/blog/2018-02-05-errata-for-reverse-engineering-fine-details-of-game-boy-hardware.html)).
-- [Emulation of Nintendo Game Boy](https://github.com/Baekalfen/PyBoy/blob/master/PyBoy.pdf) - Overview of the Game Boy hardware with the perspective of building an emulator.
+- [Emulation of Nintendo Game Boy](https://github.com/Baekalfen/PyBoy/blob/master/extras/PyBoy.pdf) - Overview of the Game Boy hardware with the perspective of building an emulator.
 - [DMG-01](https://rylev.github.io/DMG-01/public/book/) - An educational Gameboy Emulator in Rust and a companion book explaining its development. \*[Oh Boy! Creating a Game Boy Emulator in Rust](https://media.ccc.de/v/rustfest-rome-3-gameboy-emulator)- is a talk given at Rust Fest 18 about this.
 - [Building a Game Boy emulator in JavaScript](http://imrannazar.com/gameboy-Emulation-in-JavaScript) - Step by step tutorial.
 - [Writing a Game Boy emulator, Cinoop](https://cturt.github.io/cinoop.html)