Add comment about make_trace_span #1608

Job	Run time
cargo check (msrv) (wasm32)	16s
cargo check (aarch64-android)	21s
cargo check (msrv) (windows-latest)	1m 46s
cargo clippy (windows-latest)	3m 35s
cargo check (msrv) (macos-latest)	29s
cargo clippy (macos-latest)	1m 8s
cargo clippy (wasm32)	1m 24s
cargo doc	1m 22s
cargo check (msrv) (ubuntu-latest)	31s
cargo clippy (ubuntu-latest)	1m 42s
formatting	28s
Prime LFS Cache	3s
typos	5s
cargo test (wasm32)	21s
cargo test (windows-latest)	2m 50s
cargo test (macos-latest)	1m 17s
cargo test (ubuntu-latest)	4m 14s
	21m 52s

Provide feedback