Add diagram to README

[juecd]

WIP

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TL;DR

Added a systems diagram to the README.

Why we made these changes

To provide a visual overview of the system architecture, aiding understanding for new contributors or interested parties.

What changed?

• README.md: Added a 'Systems diagram' section, including an image illustrating the system architecture and a link to a blog post discussing WebRTC and X11 implementation decisions.

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