First of all, we'll use the nightly version of the Rust compiler.
While using this nightly version is not strictly necessary to use relm, it provides a syntax that is a bit nicer using a feature that is only available on this version.
That will be a good opportunity to learn how to install a different version of the compiler. Nightly is the unstable version of Rust; it's a version that is compiled almost every day. Some unstable features of Rust are only available on nightly. But, don't worry, we'll also see how to use relm on the stable version of Rust.
