README.md: new images, better text (#3392)

* Update images in README.md

* Add ferris image to hello_world example

* Clean up and improve README.md, with top-level link to Rerun

* Move sections around

examples/images/src/main.rs

@@ -12,7 +12,7 @@ fn main() -> Result<(), eframe::Error> {
         "Image Viewer",
         options,
         Box::new(|cc| {
-            // The following call is needed to load images when using `ui.image` and `egui::Image`:
+            // This gives us image support:
             egui_extras::install_image_loaders(&cc.egui_ctx);
             Box::<MyApp>::default()
         }),