The pip install command can be used to install Certbot.

pip install certbot

Or, a specific version of Certbot can be installed.

pip install certbot==2.6.0

Or, better yet, use a requirements.txt file.

certbot==2.6.0

And then install the packages using the requirements.txt file.

pip install --requirement requirements.txt

The pip list should then include certbot.

~]$ pip list
Package            Version
------------------ ---------
certbot              2.6.0

The certbot --version command can be used to verify that the certbot command is working.

~]$ certbot --version
certbot 2.6.0