CONTRIBUTING.md install instructions are wrong (add dev-environment.yml?)

[erikmannerfelt]

Is your feature request related to a problem? Please describe.
The current installation approach in CONTRIBUTING.md does not work.

It says to run:

git clone https://github.com/GlacioHack/geoutils.git
cd geoutils
conda create -f environment.yml  # add '-n custom_name' if you want.
conda activate geoutils  # or any other name specified above
pip install -e .

Then "pytest can be run":

pytest

This is false, as not even pytest is installed with the environment.yml!

Packages that are missing

• pytest
• pytest-xdist (kind of optional)
• sphinx
• numpydoc
• sphinx_rtd_theme
• sphinx-autodoc-typehints
• sphinxcontrib-programoutput
• flake8
• matplotlib
• pre-commit

Describe the solution you'd like
Add a dev-environment.yml with the aforementioned and base packages.

Describe alternatives you've considered
An alternative is to expand environment.yml, but this would install lots of unnecessary stuff for users that clone the latest main. A question, however, is how many users will clone the latest main? One? Two? Perhaps it's okay to just have one environment file! Dependencies are already defined in four places, so one more would be quite annoying:

• environment.yml
• setup.py
• dev-requirements.txt
• meta.yaml

My preferred fix

Add the development dependencies to environment.yml!