route.md: Add wildcard example code #4387

Job	Run time
check	2m 21s
cargo-hack	6m 36s
check-docs	29s
cargo-public-api-crates (axum)	59s
cargo-public-api-crates (axum-core)	49s
cargo-deny check (advisories)	16s
dependencies-are-sorted	46s
cargo-public-api-crates (axum-extra)	58s
cargo-deny check (bans licenses sources)	17s
Spell Check with Typos	6s
cargo-public-api-crates (axum-macros)	46s
test-docs	1m 47s
test-nightly	2m 32s
test-msrv	5m 46s
armv5te-unknown-linux-musleabi	1m 7s
test-versions (stable)	4m 5s
wasm32-unknown-unknown	24s
test-versions (beta)	4m 20s
	34m 24s

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