Clashing Code and Tutorial File Structure

Very small nitpick:

The code under [Writing addon code](https://freecad.github.io/Addon-Academy/Guides/Code/) reads like they are kept in the same file despite being taught as if they have their own files. I suggest adding import commands/comments to better align the code's implied structure to the tutorial.

Start at the Writing addon code guide page and compare the displayed code with the file structure implied by the tutorial. Add the import commands or comments described in the issue, and consider the work done when the code's presentation clearly reflects the tutorial's separate-file structure.

Written by the indexing model from the issue text.