Also copied from the hello_world example

Seems to be the same code as the hello_world example, so I just copied the semi-colon from there.

- Widget's with styles must also include a ComputedStyles component and set it to equal to your styles object.

It was a link to `chapter_5.md`, which is chapter 4. I changed it to `chapter_6.md`.

ImageSettings was removed from Bevy, startup settings are now plugin settings not resources. These changes allow the example code to compile with the recommended(required) versions of Bevy.

See: https://github.com/bevyengine/bevy/commit/5622d56be1262fce8a2d458f2b78abf1cab3ab50