Scratch has a very comprehensive wiki[1], which contains detailed explanations of even the most basic of concepts, along with example code. Now it also has built-in tutorials.

However, the real strength of Scratch is that it doesn't need any documentation or instruction. A sufficiently curious mind can learn it simply by clicking around and trying things out. The blocks only click together in valid combinations (which you can infer from the shape of the blocks), so it's literally impossible to create a syntax error.

[1] https://en.scratch-wiki.info/

Right. But when I'm in Scratch the wiki is nowhere to be found.

Everything needs documentation for a kid. Even a fork or a spoon.

Without ample examples of what you can do with the things you are just touching you make way slower progress and require much more motivation.

Just curious who would be reading that documentation. The kid?

Yeah. I as a kid read a lot. Of things you might call a documentation.

If it's human friendly and kid friendly with examples, pictures and heck, even a draggable blocks you can drag into your project kids would be all over it. Because it would be contextual. Pertaining to the thing they try to understand at the moment.

Scratch is not designed for a lonely bored kid. It's designed for a kid in the classroom following instructions.

Not just discoverable.

Have enough modules available they can start making stuff they want to actually use. Help them find opportunities to solve problems that matter to them using code.

Your average kid would much prefer to write a Twitter bot than a car parts inventory system or calendar app. (The latter being a typical CS assignment)