I build what I believe is currently the most popular (mostly for being free and solid: Cydia Impactor) simple tool for this, and will point out that apps sideboards in this fashion are extremely limited as you don't have access to basic iOS functionality that requires special profiles, such as push notifications, and you can only have up to three such apps installed on an iOS 10 device at a time, each of which will have a certificate that expires after only 7 days. (Apple has been slowly clamping down on these limits; it used to be such apps expired after 30 days, then they rate limited free app identifiers to 10 per week, then they made the apps expire after 7 days, and, most recently, you are limited to 3 total installed apps.)

Didn't F.lux try to do this and get promptly shut down by Apple for violating the Developer Agreement?

https://justgetflux.com/sideload/

Normally I would think this is a ridiculous approach, but given the purpose of the app is literally developer docs, it might just work.