Add doctest for README

[termoshtt]

From #204 (review)

[Copilot]

Pull Request Overview

This PR embeds the README into the crate documentation as a doctest and updates the example code block in the README to be ignored during doctest execution.

• Adds #[doc = include_str!(...)] to include README.md in lib.rs
• Changes the Rust code fence in README.md to disable doctest execution

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pyo3-stub-gen/src/lib.rs	Includes README.md via #[doc = include_str!(…)]
README.md	Updates code fence annotation for the Rust example

Comments suppressed due to low confidence (1)

README.md:98

• The code fence uses rust:ignore, which isn’t a valid doctest directive. Replace it with rust,ignore or rust,no_run to properly disable example execution.

```rust:ignore