You're asking whether you are allowed to create a walkthrough mod? Mods are allowed, yes, as long as they are not malicious of course. These mods already have guidance functionalities, so you should have a look at them first before you go reinvent the wheel:
Okay, though I don't think that's something the dev wants to take upon himself. He already has enough to do developing just the game itself; updates are already infrequent enough. The community has made the mods I listed, use those if you want a built-in walkthrough! Though I doubt that the base game itself will have a built-in walkthrough at any point in the future.