Expand contributor's guide

CONTRIBUTING.md

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 # Contributing
 
 Welcome! As a [Jupyter](https://jupyter.org) project, we follow the [Jupyter contributor guide](https://jupyter.readthedocs.io/en/latest/contributor/content-contributor.html).
+
+Make sure to also follow [Project Jupyter's Code of Conduct](https://github.com/jupyter/governance/blob/master/conduct/code_of_conduct.md)
+for a friendly and welcoming collaborative environment.
+
+This guide was adapted from the [contributing guide in the main `jupyterhub` repo.](https://github.com/jupyterhub/jupyterhub/blob/master/CONTRIBUTING.md)
+
+## Setting up a development environment
+
+JupyterHub requires Python >= 3.5.
+
+As a Python project, a development install of JupyterHub follows standard practices for installation and testing.
+
+Note: if you have Docker installed locally, you can run all of the subsequent commands inside of a container after you run the following initial commands:
+
+```
+./ci/docker-ldap.sh
+docker run -v $PWD:/usr/local/src --workdir /usr/local/src --net=host --rm -it python:3.6 bash
+```
+
+1. Do a development install with pip
+
+    ```bash
+    cd ldapauthenticator
+    python3 -m pip install --editable .
+    ```
+
+1. Install the development requirements,
+   which include things like testing tools
+
+    ```bash
+    python3 -m pip install -r dev-requirements.txt
+    ```
+1. Set up pre-commit hooks for automatic code formatting, etc.
+
+    ```bash
+    pre-commit install
+    ```
+
+    You can also invoke the pre-commit hook manually at any time with
+
+    ```bash
+    pre-commit run
+    ```
+
+To clean up your development LDAP deployment, run:
+```
+docker rm -f ldap
+```
+
+## Contributing
+
+JupyterHub has adopted automatic code formatting so you shouldn't
+need to worry too much about your code style.
+As long as your code is valid,
+the pre-commit hook should take care of how it should look.
+You can invoke the pre-commit hook by hand at any time with:
+
+```bash
+pre-commit run
+```
+
+which should run any autoformatting on your code
+and tell you about any errors it couldn't fix automatically.
+You may also install [black integration](https://github.com/ambv/black#editor-integration)
+into your text editor to format code automatically.
+
+If you have already committed files before setting up the pre-commit
+hook with `pre-commit install`, you can fix everything up using
+`pre-commit run --all-files`.  You need to make the fixing commit
+yourself after that.
+
+## Testing
+
+It's a good idea to write tests to exercise any new features,
+or that trigger any bugs that you have fixed to catch regressions.
+
+You can run the tests with:
+
+```bash
+pytest -v
+```
+
+The tests live in `ldapauthenticator/tests`.
+
+When writing a new test, there should usually be a test of
+similar functionality already written and related tests should
+be added nearby.
+
+When in doubt, feel free to ask.