Auto merge of #42414 - frewsxcv:frewsxcv/improve-cow-docs, r=QuietMisdreavus
Auto merge of #42414 - frewsxcv:frewsxcv/improve-cow-docs, r=QuietMisdreavus

Improve `Cow` method doc examples.

None

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