Document [pytest] configuration in pytest.toml / .pytest.toml #261

The README documents two configuration styles:

• [tool.pytest_env] for pyproject.toml
• [pytest_env] for pytest.toml / .pytest.toml

However, pytest.toml and .pytest.toml can also contain pytest configuration directly under the [pytest] table, and pytest-env options can be configured there, for example:

[pytest]
env = [
    "HOME=~/tmp",
    "RUN_ENV=test",
]

The current INI configuration format section shows the equivalent configuration for pytest.ini and pyproject.toml, but does not show or mention the pytest.toml / .pytest.toml form.

It would be useful to document this explicitly, so users do not get the impression that pytest.toml must use the plugin-specific [pytest_env] table.

For example, the INI-style section could include:

# pytest.toml / .pytest.toml
[pytest]
env = [
    "HOME=~/tmp",
    "RUN_ENV=test",
]

This would also clarify the distinction between the plugin-specific [pytest_env] TOML format and pytest-native configuration passed through [pytest].