docs: Added Multi-Page App example using 'root'

[TheVirtuoid]

Description

Documentation change in the 'Building For Production' page, 'Multi-Page App' section:

When using the root option, it may not be clear to beginners that the root directory needs to be included within the resolve() function. Otherwise, running the build process will error out due to the HTML files not being found.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[patak-dev]

Thanks for taking the time to improve the docs. In this particular case I don't know if we should add a full example, as it may distract the reader from the main content. Maybe we could just add a single line saying something like

If you specify a different root, remember that __dirname will still be the folder of your vite.config.js file when resolving the input paths

[TheVirtuoid]

@patak-js Thanks. I agree, we can remove the extra example. I have made that change, but added an extra sentence that gives a hint as to what a developer needs to change.