Add some Vec <-> VecDeque documentation
Add some Vec <-> VecDeque documentation

These are more than just `.into_iter().collect()`, so talk about some of their nuances.

aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust