Update primitive-types.md
Update primitive-types.md

Simplify explanation and rephrase as per @GuillaumeGomez's suggestion.
aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,GBGamer/rust,graydon/rust,graydon/rust