Package Resolution Failed

[VictorPuga]

I am trying to add this as a package dependency in Xcode, but it throws an error that the Package.swift is lacking the minimum toolchain version.

I am aware that this project is written with Swift 3.

the manifest is missing a Swift tools version specification; 
consider prepending to the manifest '// swift-tools-version:5.4.0' to specify the current 
Swift toolchain version as the lowest Swift version supported by the project; 
if such a specification already exists, consider moving it to the top of the manifest, 
or prepending it with '//' to help Swift Package Manager find it