MEAI docs: Updating JavaScript libraries included in the Templates

[jeffhandley]

The Microsoft.Extensions.AI.Templates AIChatWeb project template includes JavaScript library snapshots for DOMPurify, PDF.js, and Marked. We need to include in our documentation for customers instructing them how to update the dependency. This should be as apparent as possible, in documentation and probably in the template's output via code comments or content in the README.

It is the customers' responsibility to update after the project is created, but we need to give guidance.