docs(gpui): point examples at the moon-gpui package

[kirillDevPro]

What & why

crates/moon-gpui/examples/README.md still said to run examples from a Zed checkout with cargo run -p gpui --example hello_world. The package in this workspace is moon-gpui. cargo run -p gpui --example fails with package(s) gpui not found. cargo run -p moon-gpui --example lists the examples, including a11y and gpu_canvas, which the index never mentioned.

a11y sets AccessKit roles on a heading, a spin button, a switch, and a list, and exposes increment, decrement, and toggle actions. gpu_canvas drives a gpu_canvas element that returns GpuFrameDecision::RequestPresent on a 500 ms interval and does not dirty the view.

The same -p gpui command was in the module comments of a11y.rs, testing.rs, and move_entity_between_windows.rs. Those comments now name moon-gpui. The Linux feature flags gpui_platform/wayland and gpui_platform/x11, and test-support, are unchanged and still exist on the dev-dependency.

A clean-context review compared the new sentences with Cargo.toml, a11y.rs, and gpu_canvas.rs and found each claim true. Nothing was dropped.

How to verify

Markdown and //! comments only. No logic, signatures, or tests changed.

cargo run -p gpui --example
cargo run -p moon-gpui --example

The first command fails because no package is named gpui. The second lists hello_world, a11y, and gpu_canvas.