First code example regarding stdin emits a warning

[dexygen]

What needs to be fixed?

The very first code example on the page in the docs regarding stdin is confusing because, using Rust 1.6.2, when executing the line with the comment // We get Stdin here appended, the warning "variable does not need to be mutable" is emitted.

Page(s) Affected

https://doc.rust-lang.org/std/io/struct.Stdin.html

Suggested Improvement

If the need for a mutable became unnecessasry as of a particular Rust version, perhaps add a comment to that effect

[ghost]

If the need for a mutable became unnecessasry as of a particular Rust version, perhaps add a comment to that effect

Yes, this mut was definitely required in an older version... I don't know which one, if it matters.