docs: fix missing includes in code example

[RedSparrowEU]

Description of Change

Close #35157.

This change adds the required lines to the sample code so that it can be used directly via copy/paste without any hassle.

Checklist

• PR description included and stakeholders cc'd
• relevant documentation is changed or added
• PR release notes describe the change in a way relevant to app developers, and are [capitalized, punctuated, and past tense]

Release Notes

Notes: none

[welcome]

💖 Thanks for opening this pull request! 💖

We use semantic commit messages to streamline the release process. Before your pull request can be merged, you should update your pull request title to start with a semantic prefix.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add app.isPackaged() method
• docs: app.isDefaultProtocolClient is now available on Linux

Things that will help get your PR across the finish line:

• Follow the JavaScript, C++, and Python coding style.
• Run npm run lint locally to catch formatting errors earlier.
• Document any user-facing changes you've made following the documentation styleguide.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[welcome]

Congrats on merging your first pull request! 🎉🎉🎉

[release-clerk]

No Release Notes