Rollup merge of #66114 - golddranks:improve_thread_docs, r=Centril
Rollup merge of #66114 - golddranks:improve_thread_docs, r=Centril

Improve std::thread::Result documentation

Thanks to @dtolnay for pointing out the different premise of the contents of the `Err` variant in `std::thread::Result` WRT normal error handling.

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