Expand the README with key feature examples

[ryanfowler]

Summary

• Add a short positioning paragraph that explains fetch beyond basic HTTP requests.
• Add runnable examples for common API work, DNS and TLS inspection, timing, WebSockets, gRPC, image rendering, pager control, and clipboard output.
• Make request-body examples explicit about -m POST so the README does not imply bodies change the default method.

Testing

• Not run (not requested).