Auto merge of #40765 - pirate:patch-3, r=aturon
Auto merge of #40765 - pirate:patch-3, r=aturon

Add contribution instructions to stdlib docs

Generally programming language docs have instructions on how to contribute changes.

I couldn't find any in the rust docs, so I figured I'd add an instructions section, let me know if this belongs somewhere else!

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