Docs: Enable RTD on tf-m-extras

Added files required for the tf-m-extras documentation to be displayed on Read the Docs.

Change-Id: I813589f566b58834dc75142b7a92349589d8da87
Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/docs/index.rst b/docs/index.rst
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+################################
+Trusted Firmware-M Extras
+################################
+
+.. raw:: html
+
+The Trusted Firmware-M (TF-M) Extras repository is the extension of the TF-M
+main repository to host the examples, demonstrations, third-party modules,
+third-party secure partitions, etc.
+
+*******
+License
+*******
+
+The default license of new source code in this repository is :doc:`BSD 3-clause <license>`.
+
+Some source files are contributed by the third-parties or derived from the
+external projects. A license file should be included in the root folder of these
+source files if it has a different license.
+
+****************
+Folder Structure
+****************
+
+- `examples`: This folder hosts the examples and demos for TF-M.
+- `partitions`: This folder hosts the supplementary or third-party secure
+  partitions for TF-M.
+
+*****************************
+Contribute to this repository
+*****************************
+
+Refer to `contributing process <https://trustedfirmware-m.readthedocs.io/en/latest/contributing/contributing_process.html>`_
+for the TF-M general contribution guideline.
+
+Please contact `TF-M development mailing list <https://lists.trustedfirmware.org/mailman3/lists/tf-m.lists.trustedfirmware.org>`_
+for any question.
+
+.. note::
+   If your contribution consists of pre-bulit binaries, please upload your
+   binary components to
+   `Trusted Firmware binary repository (tf-binaries) <https://git.trustedfirmware.org/tf-binaries.git/about/>`_.
+   This respository accepts source files only.
+
+Additional requirements
+=======================
+
+- It is expected and strongly recommended to integrate and test your
+  example/secure partition with TF-M latest release, to enable new features and
+  mitigate known security vulnerabilities.
+
+- List the example and secure partition in
+  :doc:`example readme <examples/examples_readme>` and
+  :doc:`secure partition readme <partitions/partitions_readme>` respectively.
+
+   - Each example/secure partition shall specify the following information
+
+      - A brief description
+      - Maintainers with their contact emails
+      - If the example/secure partition is not integrated or tested with the
+        latest TF-M release, specify the TF-M version/commit ID tested with.
+
+   - Each example/secure partition shall follow the structure below
+
+     .. code-block:: rst
+
+        Folder name
+        ===========
+
+        Description
+        -----------
+        Simple description
+
+        Maintainers
+        -----------
+        Maintainer list and emails
+
+        TF-M version
+        ------------
+        Optional. Specify the TF-M version/commit ID if it is not integrated or
+        test with latest TF-M release.
+
+.. toctree::
+  :caption: Overview
+  :maxdepth: 1
+  :hidden:
+
+  Partitions <partitions/index>
+  Examples <examples/index>
+
+.. toctree::
+  :caption: Links
+  :maxdepth: 1
+  :hidden:
+
+  Trusted Firmware-M <https://trustedfirmware-m.readthedocs.io/en/latest/>
+
+--------------
+
+*Copyright (c) 2021-2022, Arm Limited. All rights reserved.*