First, you need to install Python 3 and PIP (if not already present on your system):
$ sudo apt-get install python3-pip
You might need to update PIP right away
$ pip3 install -U pip
Then, install pipenv
$ pip install --user -U pipenv
The suggested way to get sphinx-versions is to use pipenv. Simply run this command, from your current project:
pipenv install sphinx-versions
Lastly you can also just clone the repo and install from it. Usually you only need to do this if you plan on :ref:`contributing <contributing>` to the project.
git clone git@github.com:Smile-SA/sphinx-versions.git
cd sphinx-versions
python setup.py install