Fix package name in pip install command

[ksdme]

The project seems to reside at https://pypi.org/project/tetraframework/ and running the command in the doc fails with

  Could not find a matching version of package tetra-framework

  at /usr/local/lib/python3.9/site-packages/poetry/console/commands/init.py:381 in _find_best_version_for_package
      377│         )
      378│
      379│         if not package:
      380│             # TODO: find similar
    → 381│             raise ValueError(
      382│                 "Could not find a matching version of package {}".format(name)
      383│             )
      384│
      385│         return package.pretty_name, selector.find_recommended_require_version(package)

[samwillis]

Thanks Kilari!