Docs: overview, architecture, design, modeling

Issue-ID: CPS-268
Change-Id: I31480a9a6186af0ddedae4f0eca06a744a2e2d64
Signed-off-by: Ruslan Kashapov <ruslan.kashapov@pantheon.tech>
diff --git a/docs/design.rst b/docs/design.rst
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+.. This work is licensed under a Creative Commons Attribution 4.0 International License.
+.. http://creativecommons.org/licenses/by/4.0
+
+.. DO NOT CHANGE THIS LABEL FOR RELEASE NOTES - EVEN THOUGH IT GIVES A WARNING
+.. _design:
+
+
+CPS Design
+##########
+
+.. toctree::
+   :maxdepth: 1
+
+Offered APIs
+============
+
+CPS supports the public APIs listed in the link below:
+
+:download:`OpenApi Specification <api/swagger/openapi.yml>`
+
+Exposed API
+-----------
+
+The standard for API definition in the RESTful API world is the OpenAPI Specification (OAS).
+The OAS 3, which is based on the original "Swagger Specification", is being widely used in API developments.
+
+Specification can be accessed using following URI:
+
+.. code-block:: bash
+
+  “http://<hostname>:<port>/v3/api-docs?group=cps-docket”