Edit lessons to set expectations periodically

When people start learning how to code, they come with certain expectations and it's important that we help them understand the time it'll take and help them see that they're doing well and it's normal if some things are still fuzzy.

In part so they don't get frustrated with themselves when they don't get the results they'd like as fast as they imagined.

In Learn GDScript we could achieve this by having sentences periodically in lessons that help people understand:

1. What they understand by now (serves as super short lesson recaps).
2. What is normal to still be unclear about.
3. How long it will take or what it will take for something to become comfortable or natural (e.g., you will need to use this concept in practice in several projects before you're very comfortable with it).

E.g. things like:

> Don't worry if it's not clear yet, it's a tricky concept to wrap your head around, you'll need to revisit it multiple times to understand it fully.

In particular, we should strive to make it clear that you're not going to come out a coder from this app. We do mention this at the start and on GDSchool but we probably need to recap toward the end that the point is to learn some ABCs of code and syntax concepts so that you can go on and learn Godot and gamedev concepts more comfortably.