docs: Add documentation to describe how to install the package

This chapter explains how to install the crostests package and build its
documentation.
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

docs/source/install.rst

@@ -4,3 +4,54 @@ Installation
 
 Requirements
 ============
+
+``crostests`` has the following strict requirements:
+
+- `Python <https://www.python.org/>`_ 3.5 or later
+
+- `unittest2 <https://docs.python.org/3/library/unittest.html>`_ 1.1.0 or later
+
+Installing ``crostests``
+========================
+
+To install ``crostests`` with `pip <https://pip.pypa.io>`_, run::
+
+    pip install git+https://gitlab.collabora.com/chromiumos/crostests.git
+
+Testing an Installed ``crostests``
+----------------------------------
+
+The easiest way to test if your installed version of ``crostests`` is running
+correctly is to use one of the runner function::
+
+    python3 -m cros.runners.lava_runner
+
+The tests should run and print out the result.
+
+Building Documentation
+----------------------
+
+Dependencies
+^^^^^^^^^^^^
+
+Building the documentation requires the ``crostests`` source code and some
+additional packages. The easiest way to install the extra dependencies for
+documentation is to install the distribution packages:
+
+* `Sphinx <http://www.sphinx-doc.org/>`_ - the main package we use to build
+  the documentation
+* `python3-sphinx-rtd-theme <https://github.com/readthedocs/sphinx_rtd_theme>`_ -
+  the default 'bootstrap' theme used by ``crostests``
+
+Building
+^^^^^^^^
+
+The easy way is to execute the command (from the ``crostests`` source
+directory)::
+
+    cd docs
+    make html
+
+The documentation will be built in the ``docs/build/html`` directory, and can
+be read by pointing a web browser to ``docs/build/html/index.html``.
+