Needs basic overview documentation

The documentation / readme doesn't say much
- What type of container is the javascript running in?
- What does the media bridge do?
- How is the code organized? What is in the different directories?
- What features are different/missing compared to FF, Chromium, Chrome?
- Is the architecture diagram relevant for Android & iOS?
- What are the main features?

A few lines added to the front page would go a long way.

Start with the documentation/README front page and review the existing architecture diagram and directory descriptions. Add a concise overview addressing the JavaScript container, media bridge, code organization, browser differences, Android and iOS relevance, and main features; done means these questions are answered on the front page.

Written by the indexing model from the issue text.