Integrate the new SwiftPM add-dependency command in the "Use this package" modal

[daveverwer]

Discussed in #3188

^{Originally posted by MahdiBM July 5, 2024}
We have a new add-dependency command in Swift 6:

swift package add-dependency https://github.com/DiscordBM/DiscordBM --from 1.12.0

SPI's "Use this package" view should include this, with a small note that it requires Swift 6 CLI.

crates.io also references these commands, which reminded me that we recently got them in Swift too, so SPI can also do that: