Not sure when it was last updated, but for at least the past few years, any time I tap to install an application I got from a dev's site or whatever, it basically says "hey, you haven't given permission to install apps from this source. doing so might not be safe, etc." with a link/button to take you to the menu with the relevant toggle.
As an end user, it's akin to typing my root password to clicking "accept" on Windows UAC. I can still install it just fine, but I need to give permission and check the box accepting responsibility.
Whether that's enough to protect someone from doing something unwise can be debated, but it's not something you'd really need instructions for.