Add basic info on how to preview a page

[linawolf]

We recommend submitting changes and suggestions via pull requests. For small changes you
can use the "Edit on GitHub" button which is found at the top of every documentation
page.

For more information on how you can contribute and help improve TYPO3's
documentation, visit the "How to document guide": https://docs.typo3.org/m/typo3/docs-how-to-document/main/en-us/WritingDocsOfficial/Index.html

Current behavior

A clear and concise description of what the problem is.

Expected behavior/output

A clear and concise description of what you expect to happen.

Links

One or more links to the documentation page (if available), preferably to the
relevant section. If applicable, also link to other resources which might be
helpful to better understand your proposal.

TYPO3 versions

[e.g. 11, 12]

Possible Solution

Only if you have concrete suggestions to solve the issue.

Additional context

Add any other context or screenshots about your proposal here.