build(ariadne): vendor clap

third_party/crates/clap-4.6.6/examples/cargo-example-derive.md

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+For more on creating a custom subcommand, see [the cargo
+book](https://doc.rust-lang.org/cargo/reference/external-tools.html#custom-subcommands).
+The crate [`clap-cargo`](https://github.com/crate-ci/clap-cargo) can help in
+mimicking cargo's interface.
+
+The help looks like:
+```console
+$ cargo-example-derive --help
+Usage: cargo <COMMAND>
+
+Commands:
+  example-derive  A simple to use, efficient, and full-featured Command Line Argument Parser
+  help            Print this message or the help of the given subcommand(s)
+
+Options:
+  -h, --help  Print help
+
+$ cargo-example-derive example-derive --help
+A simple to use, efficient, and full-featured Command Line Argument Parser
+
+Usage: cargo example-derive [OPTIONS]
+
+Options:
+      --manifest-path <MANIFEST_PATH>  
+  -h, --help                           Print help
+  -V, --version                        Print version
+
+```
+
+Then to directly invoke the command, run:
+```console
+$ cargo-example-derive example-derive
+None
+
+$ cargo-example-derive example-derive --manifest-path Cargo.toml
+Some("Cargo.toml")
+
+```