Fixed #26416 -- Fixed references to previous tutorial numbers in docs/intro/reusable-apps.txt.

Advanced tutorial: How to write reusable apps

=============================================

This advanced tutorial begins where :doc:`Tutorial 6 </intro/tutorial06>`

This advanced tutorial begins where :doc:`Tutorial 7 </intro/tutorial07>`

left off. We'll be turning our Web-poll into a standalone Python package

you can reuse in new projects and share with other people.

If you haven't recently completed Tutorials 1–6, we encourage you to review

If you haven't recently completed Tutorials 1–7, we encourage you to review

these so that your example project matches the one described below.

Reusability matters