Rollup merge of #84067 - rust-lang:steveklabnik-patch-1, r=joshtriplett
Rollup merge of #84067 - rust-lang:steveklabnik-patch-1, r=joshtriplett

clean up example on read_to_string

This is the same thing, but simpler.

This came out of a comment from a user: https://news.ycombinator.com/item?id=25318117 but rather than hide the signature of main, I think a `use` plus not including the `'static` makes more sense.

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