Update instructions for importing game.dart

[surfmuggle]

Clarified instructions for importing game.dart in main.dart.

• why: For a beginner a command what to do is helpfull.
• Issues fixed: Clearer instructions what has to be done

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

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[gemini-code-assist]

Code Review

This pull request updates the widget fundamentals tutorial documentation to provide more detailed instructions for importing the game logic file into the main application. A review comment identifies a line exceeding the 80-character limit for semantic line breaks and suggests splitting it for better readability and style compliance.

[gemini-code-assist]

This line exceeds the 80-character limit for semantic line breaks as specified in the PR checklist. Breaking the instruction into two lines improves readability and ensures adherence to the project's documentation standards.

Suggested change

	1. Import the file in your `lib/main.dart` file. Open `lib/main.dart` and add this line `import 'game.dart';` after the first import.
	1. Import the file in your `lib/main.dart` file.
	Open `lib/main.dart` and add `import 'game.dart';` after the first import.

References

1. Use semantic line breaks of 80 characters or fewer. ^(link)