Add "lxml" to the packages for pip to install into the virtual environment.

Piyush's pyccuracy tests will use it.
diff --git a/GettingStarted.wiki b/GettingStarted.wiki
index a2708df..489e2b1 100644
--- a/GettingStarted.wiki
+++ b/GettingStarted.wiki
@@ -26,7 +26,7 @@
 git clone http://code.google.com/p/soc/
 cd soc
 virtualenv venv
-venv/bin/pip install -U setuptools
+venv/bin/pip install -U lxml setuptools
 venv/bin/python bootstrap.py
 bin/buildout
 bin/gen-app-yaml local-devel