Add more crate-level docs #111

Job	Run time
Cargo check	16s
Clippy lint checks	20s
Code formatting checks	20s
Build with each feature combination	21s
Minimal dependency versions build	23s
Machete dependencies checks	1m 55s
Build & test (nightly, ubuntu-latest)	23s
Build & test (stable, ubuntu-latest)	23s
Build & test (stable, macos-latest)	27s
Build & test (nightly, macos-latest)	26s
Build & test (nightly, windows-latest)	51s
Build & test (stable, windows-latest)	58s
Build & test (1.88, windows-latest)	53s
Build & test (1.88, ubuntu-latest)	21s
Build & test (1.88, macos-latest)	27s
Miri test	55s
	9m 39s

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