Make instructions about copying kernel module more clear.

Change-Id: Iaed6fe6c67ab13fa888f5d682b42c39734af6f0c
diff --git a/docs/PreparingLinux.md b/docs/PreparingLinux.md
index 881f2f3..283b9ce 100644
--- a/docs/PreparingLinux.md
+++ b/docs/PreparingLinux.md
@@ -68,7 +68,14 @@
 
 At this point you can copy into the current directory additional files you may
 want in the RAM disk, for example, the kernel module built in the previous
-section. Then run the following commands:
+section. Assuming the BusyBox root directory is in the same parent directory as
+the Hafnium root directory:
+
+``` shell
+cp ../../hafnium/driver/linux/hafnium.ko .
+```
+
+Then run the following commands:
 
 ``` shell
 find . | cpio -o -H newc | gzip > ../initrd.img