Doc: add design proposal process documentation.

Add new document section for processes and new document describing the
design proposal process.

Added CMake support for status handling of design documents.
Improved update process (dependency handling) of Sphinx documentation.
Fixed issue where the intermediate document files from the build
directory were added to Sphinx output if the build directory was placed
under TF-M root directory.

Change-Id: Ie21abe120ffcb5f0a79ddf1c398eb198959878f3
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
diff --git a/docs/index.rst.in b/docs/index.rst.in
new file mode 100644
index 0000000..e2151a4
--- /dev/null
+++ b/docs/index.rst.in
@@ -0,0 +1,93 @@
+:Page authors: Gyorgy Szing <gyorgy.szing@arm.com>
+
+..
+   The build-system will copy all documents into a temporary directory tree
+   before the documentation is built.
+   This file will be copied to the top level and thus please use relative paths
+   as if this file would be in <TFM_ROOT_DIR>.
+   
+   The values between @ characters will be filled in by CMake.
+
+
+Welcome to TF-M's documentation!
+================================
+
+.. toctree::
+    :maxdepth: 2
+    :glob:
+    :hidden:
+
+    contributing
+    docs/dco
+    glossary
+    maintainers
+    docs/user_guides/tfm_sw_requirement
+    docs/user_guides/tfm_build_instruction
+    docs/coding_guide
+    docs/user_guides/tfm_user_guide
+    docs/user_guides/os_migration_guide_armv8m
+    docs/user_guides/tfm_integration_guide
+    docs/user_guides/tfm_ns_client_identification
+    docs/user_guides/tfm_secure_boot
+
+.. toctree::
+    :maxdepth: 2
+    :caption: Processes
+    :glob:
+    :hidden:
+
+    docs/processes/**
+
+.. toctree::
+    :maxdepth: 2
+    :caption: Secure services
+    :glob:
+    :hidden:
+
+    docs/user_guides/services/*
+
+.. toctree::
+    :maxdepth: 2
+    :caption: Components
+    :glob:
+    :hidden:
+
+    lib/**
+
+.. toctree::
+    :maxdepth: 2
+    :caption: Target platforms
+    :glob:
+    :hidden:
+
+    platform/**
+
+.. toctree::
+    :caption: Design documents
+    :maxdepth: 2
+    :glob:
+    :hidden:
+
+    @ACCEPTED_DD_LIST@
+
+.. toctree::
+    :caption: Draft design documents
+    :maxdepth: 2
+    :glob:
+    :hidden:
+
+    @DRAFT_DD_LIST@
+
+.. toctree::
+    :caption: Rejected design documents
+    :maxdepth: 2
+    :glob:
+    :hidden:
+
+    @REJECTED_DD_LIST@
+
+.. include:: readme.rst
+
+-----------
+
+*Copyright (c) 2019, Arm Limited. All rights reserved.*