As otk is still in a proof of concept state it is not yet packaged for any distributions. Installation thus requires you to work from source.
To start hacking on otk you can:
€ git clone https://github.com/osbuild/otk
# ...
€ python3 -m venv venv
# ...
€ . venv/bin/activate
# ...
€ pip install -e ".[dev]"
# ...
€ make external
# ...
€ pre-commit install
# ...
This will get you an activated Python virtual environment with an editable install of otk. You can then run edit source in src/ and run otk as long as your virtual environment is enabled. When you do a git commit some verification steps will run locally on the changed files.
You can read more about contributing