Doc: non C specific doxygen documentation added.

Some parts of the TF-M Reference Manual are defined/written outside of
C source files. These files have the .dox extension and have meta-data
in C coments and doxygen documentation in C doxygen comments.

Change-Id: Ia348be72acae9958f1bc65588cc4c14c8cf0c7e7
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
diff --git a/secure_fw/services/dir_services.dox b/secure_fw/services/dir_services.dox
new file mode 100644
index 0000000..7525e15
--- /dev/null
+++ b/secure_fw/services/dir_services.dox
@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2018-2019, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+//This file holds description for the current directory. This documentation
+//will be included in the Doxygen output.
+
+/*!
+\dir
+\brief Source code for secure services.
+\details The source code of each service lives in a sub-directory. In addition
+this directory holds source files defining partitioning information. These are
+generated from the templates in this directory, and partition manifest files.
+
+*/
\ No newline at end of file