Add fTPM documentation

Create documentation for the fTPM deployment and the various TPM related
components implemented in the project.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: Id06cb26d0cd3f5a1fe3542a08fadea63023ac5fb
diff --git a/docs/services/index.rst b/docs/services/index.rst
index 15e2415..0d1d30c 100644
--- a/docs/services/index.rst
+++ b/docs/services/index.rst
@@ -12,6 +12,7 @@
     block-storage/block-storage-service-description
     uefi-smm-services
     logging-service-description
+    tpm-service-description
 
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