Add a Meson example under examples/

[shenxianpeng]

Context

examples/ contains cmake/ and large-project/, and the docs reference Meson usage, but there's no dedicated examples/meson/ template like examples/cmake/. Meson users have to piece it together themselves.

Task

Add examples/meson/README.md, mirroring the structure of examples/cmake/README.md, showing:

• generating the compile database with meson setup builddir (produces builddir/compile_commands.json), and
• a matching .pre-commit-config.yaml using --compile-commands=builddir.

Then link it from examples/README.md and the "Examples" section of the main README.md.

Acceptance criteria

• examples/meson/README.md is self-contained and consistent with the CMake example.
• It's linked from examples/README.md and the root README.md.

Getting started

This is a docs-only addition; see CONTRIBUTING.md.