Document new dependencies.

Change-Id: Ic6c61c94aa5d9117f1dce06c28b93b4aad727dfe
diff --git a/docs/GettingStarted.md b/docs/GettingStarted.md
index e997ecb..3cb2833 100644
--- a/docs/GettingStarted.md
+++ b/docs/GettingStarted.md
@@ -24,7 +24,7 @@
 Install prerequisites:
 
 ```shell
-sudo apt install make libssl-dev flex bison
+sudo apt install make libssl-dev flex bison python3 python3-serial
 ```
 
 By default, the hypervisor is built with clang for a few target platforms along