Add minimal pyproject.toml to fix tox

[mgorny]

Add a minimal pyproject.toml file that fixes the following tox failure:

ERROR: missing /tmp/dparse/pyproject.toml

[yeisonvargasf]

Thank you, @mgorny; this is already covered for another PR. I apologize for arriving so late on this.

Your PRs are always welcome; thank you for taking the time to submit this change. I'll work to reduce the time to address PRs.

I'm closing this because it won't be needed.

[mgorny]

Thanks.