route.md: Add wildcard example code #4361

Job	Run time
cargo-hack	5m 3s
cargo-public-api-crates (axum)	1m 0s
check-docs	24s
cargo-public-api-crates (axum-core)	49s
check	1m 33s
cargo-deny check (advisories)	22s
cargo-public-api-crates (axum-extra)	2m 31s
cargo-deny check (bans licenses sources)	24s
dependencies-are-sorted	45s
Spell Check with Typos	6s
cargo-public-api-crates (axum-macros)	52s
test-docs	0s
armv5te-unknown-linux-musleabi	0s
test-msrv	0s
test-nightly	0s
test-versions	0s
wasm32-unknown-unknown	0s
	13m 49s

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