[WIP] Add docs for PDP testing

Change-Id: I7832c821d5923fde983621fd41b0ac4431d72645
diff --git a/index.rst b/index.rst
index 6219c74..7644781 100644
--- a/index.rst
+++ b/index.rst
@@ -43,6 +43,7 @@
 
    testing/about_system_tests
    testing/acceptance_specification
+   testing/pdp_testing
 
 .. toctree::
    :maxdepth: 1