pyproject.toml examples

[PaulRudin]

What's the problem this feature will solve?

Make pyproject.toml easier to use with pip-tools.

Describe the solution you'd like

Add more pyproject.toml examples to the docs.

The pip-tools readme recommends using pyproject.toml for new projects, but nearly all the docs and examples use .in files. It would be easier to use pyproject.toml if there were examples.