Docs: Restructure the documents

Restructure the file category to let it more friendly to users.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I7ced0e2d700ce03423e472e0098608f3445ba169
diff --git a/docs/contributing/contributing_process.rst b/docs/contributing/contributing_process.rst
new file mode 100644
index 0000000..b017c63
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@@ -0,0 +1,80 @@
+Contributing Process
+====================
+
+Contributions to the TF-M project need to follow the process below.
+
+.. Note::
+
+   Please contact :doc:`maintainers </docs/contributing/maintainers>` for any
+   questions.
+
+- Subscribe to `TF-M development
+  <https://lists.trustedfirmware.org/mailman/listinfo/tf-m>`_ if not subscribed
+  already.
+- Refer to the `Roadmap
+  <https://developer.trustedfirmware.org/w/tf_m/planning>`_ or send a mail to
+  the tf-m@lists.trustedfirmware.org to check if this work is already
+  planned/progresses elsewhere.
+- Create a task in `Phabricator
+  <https://developer.trustedfirmware.org/maniphest>`_, put as many details as
+  possible in the description. Add 'Trusted Firmware M' in the 'Tags' field.
+- For non-trivial changes, need to follow the design proposal process
+  :doc:`Design Proposal Process </docs/contributing/tfm_design_proposal_process>`
+  for the TF-M project.
+- After the design has been accepted by the maintainer(s), a corresponding
+  patch should be posted; follow guidelines below:
+
+  - Clone the TF-M code on your own machine from `TF-M git repository
+    <https://git.trustedfirmware.org/TF-M/trusted-firmware-m.git>`_.
+  - Follow the :doc:`SW Requirements </docs/getting_started/tfm_sw_requirement>`,
+    :doc:`Build Instructions </docs/getting_started/tfm_build_instruction>` and
+    :doc:`Coding Guide </docs/contributing/coding_guide>` for the TF-M project.
+  - Make your changes in logical chunks to help reviewers. Each commit should
+    be a separate review and either work properly or be squashed after the
+    review and before merging.
+  - Update documentation in docs/ folder if needed.
+  - Test your changes and add details to the commit description.
+  - The code is accepted under :doc:`DCO </docs/contributing/dco>`, Developer
+    Certificate of Origin, so you must add following fields to your
+    commit description:
+
+    .. code-block:: text
+
+       Author: Full Name <email address>
+       Signed-off-by: Full Name <email address>
+
+    .. Note::
+
+       Sign off authority needs to adhere to the [DCO](./dco.txt) rules.
+
+  - You must add a `Change-Id
+    <https://review.trustedfirmware.org/Documentation/user-changeid.html>` to
+    the commit message, which can be generated any way you like (e.g. from the
+    SHA of the commit), or use the commit hook.
+  - Create a user in the `TF-M Gerrit <https://review.trustedfirmware.org>`,
+    then add `SSH keys or HTTP credentials
+    <https://review.trustedfirmware.org/settings/>`.
+  - Submit your patch for review.
+
+    .. code-block:: shell
+
+       git push ssh://review.trustedfirmware.org:29418/TF-M/trusted-firmware-m.git HEAD:refs/for/master
+
+    or
+
+    .. code-block:: shell
+
+       git push https://review.trustedfirmware.org/TF-M/trusted-firmware-m.git HEAD:refs/for/master
+
+- Add relevant :doc:`maintainers </docs/contributing/maintainers>` for reviewing
+  the patch.
+- You may be asked to provide further details or make additional changes.
+- You can discuss further with maintainer(s) by directly over email if
+  necessary.
+- Once the change is approved by maintainers, the patch will be merged by the
+  maintainer.
+- Mark the task as 'resolved' after patch is merged.
+
+--------------
+
+*Copyright (c) 2017-2021, Arm Limited. All rights reserved.*