First,

zig fetch --save https://github.com/simalei/linenoise.zig

Then, in your build.zig,

const linenoise = b.dependency("linenoise_zig", .{});

// ...
// Assuming that `mod` is the root module of your compilation
mod.addImport("linenoise", linenoise.module("linenoise"));

// ...

And in your source code,

const linenoise = @import("linenoise");