Rollup merge of #59532 - mbrubeck:docs, r=Centril

In doc examples, don't ignore read/write results

Calling `Read::read` or `Write::write` without checking the returned `usize` value is almost always an error.  Example code in the documentation should demonstrate how to use the return value correctly.  Otherwise, people might copy the example code thinking that it is okay to "fire and forget" these methods.