Add a doc which will help tempest contributors

This patch adds a document which is supposed to help tempest
contributors to start with tobiko.

The doc mentions some big differences between tempest and tobiko.

In order to see the changed docs, please access:
Zull run -> openstack-tox-docs -> Logs tab -> docs (raw).

Change-Id: Ie757041d49199213641b347f898ea97f72c96fce

doc/source/content.rst

@@ -21,3 +21,4 @@ tree <https://opendev.org/x/tobiko/src/branch/master/doc/source>`__.
    contributor/index
    reference/index
    etc/index
+   miscellaneous/index

doc/source/miscellaneous/from-tempest-to-tobiko.rst

@@ -0,0 +1,35 @@
+.. _tobiko-from-tempest-to-tobiko:
+
+======================
+From Tempest to Tobiko
+======================
+
+*This doc might help programmers to embrace/join the Tobiko project, after having some experience with the Tempest project.*
+
+
+A few differences between Tobiko and Tempest:
+---------------------------------------------
+* Tobiko uses heat template stacks
+    * A `stack <https://docs.openstack.org/heat/latest/index.html>`_ is being created *"lazily"* (only when it is needed in the code), unlike “resource setup” in Tempest that always creates all the resources.
+
+* Tobiko re-uses its resources
+    * Tobiko will reuse the same resources in any possible test it can.
+
+      Ex: if one test will create a stack, and the same stack is going to be used in different tests, Tobiko will simply reuse it. It will also reuse the same stacks during other executions of the same Tobiko tests.
+
+* Tobiko’s tests structure:
+    * Tests do not require idempotent_id, each method which starts with the prefix “test” is considered to be a test which will be run.
+    * After a Tobiko test suite finishes, it **does not** delete Tobiko’s resources (no teardown), and this is by design.
+
+* Tobiko uses a client stack
+    * Traffic is being sent from a client stack that the tester may create (or a default one might be created).
+
+* Tobiko uses `Typing <https://docs.python.org/3/library/typing.html>`_:
+    * Mainly as a means of code readability and consistency.
+
+      But additional doc strings are welcome!
+
+* Tobiko tests workflow:
+    * Tobiko uses the following workflow for its sequential test execution process:
+
+      resource-creation->disruptive-actions->resource-verification.

doc/source/miscellaneous/index.rst

@@ -0,0 +1,29 @@
+..
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+      Convention for heading levels in Neutron lib devref:
+      =======  Heading 0 (reserved for the title in a document)
+      -------  Heading 1
+      ~~~~~~~  Heading 2
+      +++++++  Heading 3
+      '''''''  Heading 4
+      (Avoid deeper levels because they do not render well.)
+
+=============
+Miscellaneous
+=============
+
+.. toctree::
+   :maxdepth: 1
+
+   from-tempest-to-tobiko