Adding table of contents to docs longer than ~one page.

Change-Id: I3bb3afe88e5c54a3fdbed32a0a0dace1b65e85ee
diff --git a/docs/PreparingLinux.md b/docs/PreparingLinux.md
index 9654960..3332096 100644
--- a/docs/PreparingLinux.md
+++ b/docs/PreparingLinux.md
@@ -3,6 +3,8 @@
 To boot Linux, a kernel image (`vmlinuz`) and a suitable initial RAM disk
 (`initrd.img`) need to be created.
 
+[TOC]
+
 ## Build the kernel
 
 The Linux kernel for the primary VM can be built using the following