Add doc comments about why symbol_short! #3273

Job	Run time
build-fuzz	1m 49s
cargo-deny (advisories)	3m 28s
cargo-deny (bans licenses sources)	3m 12s
docs	4m 16s
build-and-test (ubuntu-latest, x86_64-unknown-linux-gnu)	7m 55s
build-and-test (macos-latest, x86_64-apple-darwin)	20m 53s
build-and-test (macos-latest, aarch64-apple-darwin)	22m 2s
build-and-test (windows-latest, x86_64-pc-windows-msvc)	19m 57s
fmt	20s
publish-dry-run	0s
rust-analyzer-compat	9m 31s
complete	1s
	1h 33m 24s

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