Move some files around

book/src/SUMMARY.md

@@ -1,10 +1,10 @@
 # Summary
 
-- [Introduction](./01_introduction.md)
-- [The Game Boy Advance hardware](./02_hardware.md)
-- [Running an example](./03_getting_started.md)
-    - [Environment setup](./03_environment_setup.md)
-        - [Linux setup](./03a_linux_setup.md)
+- [Introduction](./introduction/introduction.md)
+- [The Game Boy Advance hardware](./hardware/hardware.md)
+- [Running an example](./setup/getting_started.md)
+    - [Environment setup](./setup/setup.md)
+        - [Linux setup](./setup/linux.md)
         - [Windows setup]()
         - [Mac OS setup]()
-    - [Building the game](./03b_building.md)
+    - [Building the game](./setup/building.md)

book/src/setup/setup.md

@@ -1,4 +1,4 @@
-# Running the example
+# Environment setup
 
 Environment setup will depend on the platform you are using.
 agb's requirements are [rust nightly](https://www.rust-lang.org/) edition and the gnu binutils for `arm-none-eabi`.