rust - add comments to explain why word-count_test looks the way it does
rust - add comments to explain why word-count_test looks the way it does

stevejb71/xrust,Rust-Twin-Cities/flaming-octo-wookie,petertseng/exercism-rust,sacherjj/rust,exercism/xrust,ekse/exercism-rust,sacherjj/rust,ekse/exercism-rust,sacherjj/rust,Rust-Twin-Cities/flaming-octo-wookie,spazm/xrust,Jeff-Hostetler/xrust,exercism/xrust,medek/xrust,Jeff-Hostetler/xrust,stevejb71/xrust,pminten/xrust,petertseng/exercism-rust,pminten/xrust,petertseng/exercism-rust,medek/xrust,spazm/xrust