docs: add description about local CI tests

This page adds description how to run CI tests locally.

Signed-off-by: Michal Lenc <michallenc@seznam.cz>

Documentation/guides/citests.rst

@@ -0,0 +1,66 @@
+.. include:: /substitutions.rst
+.. _citests:
+
+=======================
+Running CI Test Locally
+=======================
+
+NuttX automatically runs continuous integration (CI) tests on 
+`simulator <https://nuttx.apache.org/docs/latest/guides/simulator.html>`__
+target when new pull request is submited. To avoid the tests failing you can
+also run them locally on your computer prior to submiting new pull request.
+This page describes the step by step manual to do so.
+
+Configuring NuttX
+=================
+
+NuttX has a simulator target that allows the user to run NuttX as a regular
+program on a computer. The simulator target with CI test is configured and
+compiled followingly.
+
+  .. code-block:: console
+
+      $ cd nuttx
+      $ ./tools/configure.sh sim:citest
+      $ make
+
+Now you can run the simulator to check the configuration was successful.
+
+  .. code-block:: console
+
+      $ ./nuttx
+      login: admin
+      password: Administrator
+
+You should see NuttX shell with built in test applications. Now you can exit
+the simulator.
+
+  .. code-block:: console
+
+      nsh> poweroff
+      $
+      $ # we're back at the Linux prompt.
+
+Running CI Tests
+================
+
+Running CI tests locally requires Minicom and Python 3.6 or newer to be
+installed on the system. Other requirements can be installed with following
+set of commands.
+
+  .. code-block:: console
+
+      $ cd tools/ci/testrun/env
+      $ pip3 install -r requirements.txt
+      $ cd ..
+      $ cd script
+
+Now you have everything prepared to run CI tests. The tests themself are run
+by following command.
+
+  .. code-block:: console
+
+      $ python3 -m pytest -m 'common or sim' ./ -B sim -P nuttx-path -L log-path -R sim -C --json=log-path/pytest.json
+
+Where nuttx-path is an absolute path to NuttX root directory and log-path is
+a user defined directory to which tests log are saved.

Documentation/guides/index.rst

@@ -17,6 +17,7 @@ Guides
   pysimcoder.rst
   customboards.rst
   customapps.rst
+  citests.rst
   zerolatencyinterrupts.rst
   nestedinterrupts.rst
   cortexmhardfaults.rst