2D Dodge The Creeps Tutorial - Remake mob timer section

**Your Godot version:**
Godot 4.0 beta 1

**Issue description:**
https://docs.godotengine.org/en/latest/getting_started/first_2d_game/05.the_main_game_scene.html#testing-the-scene
Scroll a bit upwards for the `MobTimer_timeout` section.

A header (with anchor) should be right before this string "In _on_MobTimer_timeout(), we will..." since that is a huge wall of text and there is suddenly a lot to process in an otherwise easy-to-understand tutorial.

[This](https://github.com/godotengine/godot-docs/issues/6231) must be merged before a remake of this intimidating paragraph is remade.

Generally, it's better to add 1 or 2 more paragraphs to explain PI used as direction and perpendicular. The problem is mainly that its a huge wall of text and by the time you read it all, the start of the code is linked to the start of the wall of text. There should be 4 seperate codeblocks with a tiny explanation of what each codeblock does (like most of the Godot docs). So I suggest first of all to split velocity and add_child to its own section at the very end. And right after the header of the timeout section, the direction/location is explained, instead of trying to compress everything together.