Add missing type annotation for docs (#104) #98

Job	Run time
Check (stable, ubuntu-latest)	15s
Check (stable, macOS-latest)	20s
Check (stable, windows-latest)	55s
Check (beta, ubuntu-latest)	17s
Check (beta, macOS-latest)	19s
Check (beta, windows-latest)	49s
Check (nightly, ubuntu-latest)	14s
Check (nightly, macOS-latest)	19s
Check (nightly, windows-latest)	52s
Clippy (stable)	16s
Test Suite (stable, ubuntu-latest)	20s
Clippy (beta)	16s
Test Suite (stable, macOS-latest)	31s
Clippy (nightly)	22s
Test Suite (stable, windows-latest)	57s
Test Suite (beta, ubuntu-latest)	21s
Test Suite (beta, macOS-latest)	25s
Test Suite (beta, windows-latest)	42s
Test Suite (nightly, ubuntu-latest)	19s
Test Suite (nightly, macOS-latest)	25s
Test Suite (nightly, windows-latest)	46s
	10m 0s

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