Add docs for setting up a developer environment

docs/contributing/dev-setup.rst

@@ -0,0 +1,65 @@
+.. _contributing_dev_setup:
+
+Setting up Development Environment
+==================================
+
+The easiest & safest way to develop & test TLJH is with `Docker <https://www.docker.com/>`_.
+
+#. Install Docker Community Edition by following the instructions on
+   `their website <https://www.docker.com/community-edition>`_.
+
+#. Clone the git repo (or your fork of it).
+#. Build a docker image that has a functional systemd in it.
+
+   .. code-block:: bash
+
+      sudo docker build -t tljh-systemd .
+
+#. Run a docker container with the image in the background, while bind mounting
+   your TLJH repository under ``/srv/src``.
+
+   .. code-block:: bash
+
+      docker run \
+        --privileged \
+        --detach \
+        --name=tljh-dev \
+        --publish 12000:80 \
+        --mount type=bind,source=$(pwd),target=/srv/src \
+        tljh-systemd
+
+#. Get a shell inside the running docker container.
+
+   .. code-block:: bash
+
+      docker exec -it tljh-dev /bin/bash
+
+#. Run the installer! The container image is already set up to default to a
+   ``dev`` install, so it'll install from your local repo rather than from github.
+
+   .. code-block:: bash
+
+      bash /srv/src/installer/install.bash
+
+   The primary hub environment will also be in your PATH already for convenience.
+
+#. You should be able to access the JupyterHub from your browser now at
+   `http://localhost:1200 <http://localhost:12000>`_. Congratulations, you are
+   set up to develop TLJH!
+
+#. Make some changes to the repository. You can test easily depending on what
+   you changed.
+
+   * If you changed the ``installer/install.bash`` script or any of its dependencies,
+     you can test it by running ``bash /srv/src/installer/install.bash``.
+
+   * If you changed the ``tljh/installer.py`` code (or any of its dependencies),
+     you can test it by running ``python3 -m tljh.installer``.
+
+   * If you changed ``tljh/jupyterhub_config.py``, ``tljh/configurer.py``,
+     ``/opt/tljh/config.yaml`` or any of their dependencies, you only need to
+     restart jupyterhub for them to take effect. ``systemctl restart jupyterhub``
+     should do that.
+
+:ref:`troubleshoot_logs` has information on looking at various logs in the container
+to debug issues you might have.