Docs: Update docs to reflect migration of test and app

Change-Id: I5c8aacdf417a5565641d69df1ab0dbe1525ec063
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/docs/design_documents/tfm_its_service.rst b/docs/design_documents/tfm_its_service.rst
index c2315ea..a9c71b7 100644
--- a/docs/design_documents/tfm_its_service.rst
+++ b/docs/design_documents/tfm_its_service.rst
@@ -62,6 +62,8 @@
 ==============
 The code structure of the service will be as follows:
 
+TF-M repo:
+
 ``interface/``
 
 - ``include/psa/internal_trusted_storage.h`` - PSA ITS API
@@ -81,6 +83,8 @@
 - ``flash_fs/`` - Filesystem
 - ``flash/`` - Flash interface
 
+tf-m-tests repo:
+
 ``test/suites/its/``
 
 - ``non_secure/psa_its_ns_interface_testsuite.c`` - Non-secure interface tests