Update documentation to use `from()` to initialize `HashMap`s and `BTreeMap`s#91482

Merged

bors merged 3 commits intorust-lang:masterfrom

JosephTLyons:update-HashMap-and-BTreeMap-documentation

Dec 11, 2021

Commits on Dec 2, 2021

Use `HashMap::from()` instead of using `HashMap::new()` with `HashMap::insert()`
JosephTLyons
committed
Use `BTreeMap::from()` instead of using `BTreeMap::new()` with `BTreeMap::insert()`
JosephTLyons
committed

Commits on Dec 3, 2021

Make `HashMap`s mutable again
JosephTLyons
committed