updated readme

Author: AlbertoZaupa

README.md

@@ -4,12 +4,13 @@
 
 - The kernel source code lives in the [kernel](kernel) folder.
 - The [test_app](test_app) contains an application to run tests on qemu.
+- The [build](build) folder is used to build PiOS as a static library (more on that in the next section).
 
 ## Building the kernel
 
 Pios is provided as a static library, issue the following commands to build it (assuming you are currently in the root directory of the project):
 ```
-$ cd kernel
+$ cd build
 $ cargo build --release
 $ cp target/thumbv7em-none-eabi/release/libpios.a ..
 $ cd ..