The new add-ons for GAS don't support installable triggers yet ("But keep the restrictions in mind"), but the old sheets still do (well mine still work). But I can't imagine you can deploy anything via the old script gallery anymore.
So I'd update your script to programmatically create the triggers onInstall() and create a demo version of an old spreadsheet that users could take a copy of. Then keep an eye on installable triggers coming to add-ons when you can deploy it as one of them.