Update README.md

Author: SamyPesse

chapter9/README.md

@@ -1,2 +1,13 @@
 # Memory management: physical and virtual
 
+The kernel knows the size of the physical memory available thanks to [Grub](../Chapter-3/README.md).
+
+In our implementation, the first 8 megabytes of physical memory will be reserved for use by the kernel and will contain:
+
+- The kernel
+- GDT, IDT et TSS
+- Kernel Stack
+- Some space reserved to hardware (video memory, ..)
+- Page directory and pages table for the kernel
+
+The rest of the physical memory is freely available to the kernel and applications.