chore(proto/h2): fix module-level documentation (#3881) #3001

Job	Run time
Check Style	7s
semver	14s
Verify hyper.h is up to date	2m 14s
Test with Miri	2m 37s
features	38s
Check MSRV	2m 6s
Test stable on windows-latest	3m 30s
Test stable on macOS-latest	1m 6s
Test stable on ubuntu-latest	1m 12s
Test beta on windows-latest	2m 11s
Test nightly on windows-latest	2m 14s
Test C API (FFI)	31s
Test beta on macOS-latest	1m 11s
Test nightly on ubuntu-latest	1m 6s
Test beta on ubuntu-latest	1m 12s
Test cargo-c support (FFI)	17s
minimal-versions	43s
udeps	21s
Test nightly on macOS-latest	1m 15s
Check exposed types	55s
Build docs	20s
CI is green	3s
	26m 3s

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