Add getting started guide to README

This is a first pass. As noted in the TODO, we should expand on this
further but that's a job for another day.

Change-Id: Icd44f0665995be66eba9f292e5c030be2ced9ac4
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>

README.rst

@@ -5,23 +5,100 @@ OpenStack CodeGenerator
 Primary goal of the project is to simplify maintainers life by generating
 complete or at least parts of the code.
 
-OpenApi Schema
-==============
-
 CodeGenerator is able to generate OpenAPI specs for certain services by
-inspecting their code. This requires service package being installed in the
-environment where the generator is running. It then tries to initialize service
-application and for supported runtimes scans for the exposed operations. At the
-moment following services are covered:
+inspecting their code and API Reference (api-ref) documentation. This requires
+the service package be installed in the environment where the generator is
+running. The generator then tries to initialize the service application and for
+supported services scans for the exposed operations. At the moment the
+following services are covered:
 
 - Nova
-
 - Neutron
-
 - Cinder
-
 - Glance
-
 - Keystone
-
 - Octavia
+
+Getting started
+---------------
+
+CodeGenerator is not currently packaged on PyPI (and may never be). As a
+result, you must install from Git. For example:
+
+.. code-block:: shell
+
+    $ git clone https://opendev.org/openstack/codegenerator
+    $ cd codegenerator
+    $ virtualenv .venv
+    $ source .venv/bin/activate
+    $ pip install -e .
+
+Once installed, you can use the ``openstack-codegenerator`` for all operations.
+The ``openstack-codegenerator`` provides a number of *targets*. These
+correspond to the various steps required to get a functioning OpenAPI schema.
+The first target is the ``openapi-spec`` target. This will generate an initial
+OpenAPI schema through inspection of the chosen projects code and api-ref
+documentation.
+
+Let's generate an OpenAPI schema for the Compute service, Nova. To do this, we
+first need to install Nova in the same virtualenv that we have installed
+CodeGenerator in. Let's pull the Nova repo down locally and install it:
+
+.. code-block:: shell
+
+    $ cd ..
+    $ git clone https://opendev.org/openstack/nova
+    $ cd -
+    $ pip install \
+        -c https://releases.openstack.org/constraints/upper/master
+        -r ../nova/requirements.txt
+    $ pip install -e ../nova
+
+With Nova installed, we can now run ``openstack-codegenerator``:
+
+.. code-block:: shell
+
+    $ openstack-codegenerator \
+        --work-dir wrk --target openapi-spec --service-type compute \
+        --validate
+
+If you look in the path indicated by the ``--work-dir`` argument, you will find
+a OpenAPI schema! However, this schema is rather incomplete. That's because
+we inspected the Nova code but not the api-ref docs. To do that, we need to
+pass a path to our docs, which means we need to build the docs locally. Let's
+do this:
+
+.. code-block:: shell
+
+    $ cd ../nova
+    $ tox -e api-ref
+
+.. note::
+
+    The ``api-ref`` target *should* be consistent across projects. However,
+    it's not currently part of the `Project Testing Interface`__ so this isn't
+    guaranteed. If you find this target doesn't exist, look at your project's
+    ``tox.ini`` file for clues.
+
+    .. __: https://governance.openstack.org/tc/reference/project-testing-interface.html
+
+You should now have the documentation built in HTML format and available in the
+``api-ref/build/html`` directory. Let's change back to the ``codegenerator``
+directory and run ``openstack-codegenerator`` again, this time with an
+additional ``--api-ref-src`` argument:
+
+.. code-block:: shell
+
+    $ cde ../code-generator
+    $ openstack-codegenerator \
+        --work-dir wrk --target openapi-spec --service-type compute \
+        --api-ref-src ../nova/api-ref/build/html/index.html
+        --validate
+
+Your API documentation should now be looking much better. You'll even have
+documentation available inline.
+
+There are a variety of options available, which you can view with the
+``--help`` option.
+
+.. todo: Expand on other targets, options.