Check for updates

[wheelercj]

When Stardown is installed with Git or a zip file, users are not notified when updates are available. (They can turn on notifications for releases in the GitHub repository, but many won't want to.)

Stardown should have an option to check for updates once per day if installed with Git or zip.

const info = browser.management.getSelf();

if (info.installType === 'development') {
    // check for updates once per day if enabled
}

[wheelercj]

AMO is short for addons.mozilla.org, the Firefox extension store.

When an add-on is listed on AMO, Firefox automatically updates installed copies when a new version is listed on AMO. To enable Firefox to automatically update self-distributed add-ons, you need to include the URL where Firefox can find updates in the add-on manifest's update_url key. If the add-on does not have an update URL to check, Firefox will check AMO for a listed update. If a listed update with a higher version number is available, Firefox will distribute that version to users who have installed the self-distributed file.

— Distributing an add-on yourself | Firefox Extension Workshop

I'm not sure we should use the update_url property because users that install without using AMO might not want automatic updates.