Doesn't use libadwaita

[K4rakara]

Describe the bug
hello-world.rs is a cutting edge (:rocket:) program, and therefore should be using the best practices(:rocket:) across the board. As such, I would like to recommend that it integrate libadwaita(:rocket:) in order to take advantage of the full power(:rocket:) the GNOME(:rocket:) ecosystem has to offer(:rocket:).

To Reproduce

cargo build

Expected behavior
Libadwaita (:rocket:)

Desktop (please complete the following information):

• OS: GNOME OS 42 (:rocket:)
• Browser: GNOME Web
• Version: 42, duh (:rocket:)

Additional context
GNOME (:rocket:)

[mTvare6]

Can you make a PR, and also make sure to build it and check if it adds at least 20 more dependency(if not just inform me of how much it adds)