[DOC] Added missing Debian package to getting started guide

aarch64-linux-gnu-gcc is required (in addition to
binutils-aarch64-linux-gnu) to cross compile linux for AArch64.

Change-Id: I9d1f9f3a163d7833b9bfcdeb95488e2677e44e1b
diff --git a/docs/GettingStarted.md b/docs/GettingStarted.md
index 98c6196..7182544 100644
--- a/docs/GettingStarted.md
+++ b/docs/GettingStarted.md
@@ -22,7 +22,7 @@
 Install prerequisites:
 
 ``` shell
-sudo apt install make binutils-aarch64-linux-gnu device-tree-compiler libssl-dev flex bison
+sudo apt install make binutils-aarch64-linux-gnu aarch64-linux-gnu-gcc device-tree-compiler libssl-dev flex bison
 ```
 
 By default, the hypervisor is built with clang for a few target platforms along