As #84 got finally merged, I started wondering if that could be reused for modpacks.

Flow:

1. The modpack author enters their Modrinth pack URL and current version (for point of comparison) in Mod Menu config
2. Update prompts should appear somewhere in title screen as toasts/icon/label
3. Ideally, when the option is enabled, Mod Menu should not check for updates of mods that are contained in the modpack (so only check for mods that are not, which the user probably added themselves). If that's too hard, I'd just disable the mod checker in my modpack altogether so that people would download modpack updates as a whole.
4. Also I'd prefer if people were not able to "click" anything and get led to the listing, but rather just nudge them to update via their launcher's methods instead.

See also: #126