Add a landing page

https://docs.microsoft.com/en-us/power-bi/developer/visuals/landing-page

> A Power BI visual’s landing page enables you to display information in your Power BI visual card, before it’s loaded with data. Here are a few examples of what a visual’s landing page can display:
>
> - Text that explains how to use the visual
> - A link to your website
> - A link to a video

Read the linked Power BI landing-page guidance first, then locate the visual entry point in this TypeScript project; the issue names no files or tests. Done means the visual displays a landing page before data loads, with explanatory text and appropriate website or video links.

Written by the indexing model from the issue text.