Doc: Add support for Sphinx documentation build.

Technical documentation of TF-M is captured in GitHub flavored
markdown files. This change add support for building HTML and
PDF output of these files using the Sphinx tool.

Change-Id: I8be11256f2c654c248b1974974a5de6190ca0fc3
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
diff --git a/docs/index.rst b/docs/index.rst
new file mode 100644
index 0000000..f88134a
--- /dev/null
+++ b/docs/index.rst
@@ -0,0 +1,81 @@
+: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 fill will be copied to the top level and thus please use relative paths
+   as if this file would be in <TFM_ROOT_DIR>.
+
+Welcome to TF-M's documentation!
+================================
+
+.. toctree::
+    :maxdepth: 2
+    :glob:
+    :hidden:
+    
+    contributing.md
+    glossary.md
+    maintainers.md
+    docs/user_guides/tfm_sw_requirement.md
+    docs/user_guides/tfm_build_instruction.md
+    docs/coding_guide.md
+    docs/user_guides/tfm_user_guide.md
+    docs/user_guides/os_migration_guide_armv8m.md
+    docs/user_guides/tfm_integration_guide.md
+    docs/user_guides/tfm_ns_client_identification.md
+    docs/user_guides/tfm_secure_boot.md
+    
+.. 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:
+    
+    docs/design_documents/*
+    
+.. toctree::
+    :caption: Draft design documents
+    :maxdepth: 2
+    :glob:
+    :hidden:
+    
+    docs/design_documents/drafts/*
+    
+.. toctree::
+    :caption: Rejected design documents
+    :maxdepth: 2
+    :glob:
+    :hidden:
+    
+    docs/design_documents/rejected/*
+
+.. mdinclude:: readme.md
+
+-----------
+
+:Copyright: Copyright (c) 2019, Arm Limited. All rights reserved.