Add basic CI about dlfile

[cN3rd]

Hi, nice project you have here. Came here from your reddit post.

For basic CI, you could use the following recipes from the actions-rs github project:
https://github.com/actions-rs/meta/blob/master/recipes/quickstart.md - generic CI that runs tests, rustfmt, clippy tests, etc.
https://github.com/actions-rs/meta/blob/master/recipes/security-audit.md - for running cargo-audit as a cron job

I don't mind contributing the relevant scripts myself (along with any adjustments) but I cannot commit to fully maintain it further in the future.

[insanitybit]

Hi! Thanks so much, that's already super helpful. I'd happily accept a PR and commit to maintenance, or I can take a swing at implementing these myself this upcoming weekend.