Add platform certification documentation

Adds documents about the TS project relationship with PSA Certified
and SystemReady certification programmes.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I7e8294bd3a9a2c8c2b4bad2e2ca8b2f26cb157b7
diff --git a/docs/certification/index.rst b/docs/certification/index.rst
index 067f6e6..58f8f1f 100644
--- a/docs/certification/index.rst
+++ b/docs/certification/index.rst
@@ -1,12 +1,24 @@
 Platform Certification
 ======================
+Various certification programmes exist to help platform vendors produce hardware
+and firmware that meets defined requirements for security and feature compatibility.
+By conforming to a set of testable criteria, platform vendors can make assurances to
+customers about the capabilities and security of their products.
+
+The Trusted Services project is an upstream source for service related components
+that can be integrated into platform firmware. Many of these components are important
+building blocks for meeting certification requirements. Reuse of components by
+downstream platform integration projects will help drive quality and security
+improvements, especially in areas covered by relevant certification programmes.
+
+Currently, the following certification programmes have been adopted by downstream
+platform integration projects:
 
 .. toctree::
     :maxdepth: 1
-    :caption: Contents:
 
-    psa
-    ff-a
+    psa-certified
+    system-ready
 
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