Add missing links to source code (#3770)

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Closes <https://github.com/emilk/egui/issues/THE_RELEVANT_ISSUE>.

crates/egui_demo_lib/src/demo/about.rs

@@ -51,6 +51,10 @@ impl super::View for About {
             ui.hyperlink_to("Rerun.io", "https://www.rerun.io/");
             ui.label(", a startup building an SDK for visualizing streams of multimodal data");
         });
+
+        ui.vertical_centered(|ui| {
+            ui.add(crate::egui_github_link_file!());
+        });
     }
 }
 

crates/egui_demo_lib/src/demo/highlighting.rs

@@ -21,6 +21,10 @@ impl super::Demo for Highlighting {
 
 impl super::View for Highlighting {
     fn ui(&mut self, ui: &mut egui::Ui) {
+        ui.vertical_centered(|ui| {
+            ui.add(crate::egui_github_link_file!());
+        });
+
         ui.label("This demo demonstrates highlighting a widget.");
         ui.add_space(4.0);
         let label_response = ui.label("Hover me to highlight the button!");

crates/egui_demo_lib/src/demo/layout_test.rs

@@ -113,6 +113,10 @@ impl super::View for LayoutTest {
                 }
             });
         ui.label("Resize to see effect");
+
+        ui.vertical_centered(|ui| {
+            ui.add(crate::egui_github_link_file!());
+        });
     }
 }
 

crates/egui_demo_lib/src/demo/tests.rs

@@ -468,6 +468,9 @@ impl super::Demo for WindowResizeTest {
             .default_size([250.0, 150.0])
             .show(ctx, |ui| {
                 ui.label("This window has empty space that fills up the available space, preventing auto-shrink.");
+                ui.vertical_centered(|ui| {
+                    ui.add(crate::egui_github_link_file!());
+                });
                 ui.allocate_space(ui.available_size());
             });
     }

crates/egui_demo_lib/src/demo/text_edit.rs

@@ -32,6 +32,10 @@ impl super::Demo for TextEditDemo {
 
 impl super::View for TextEditDemo {
     fn ui(&mut self, ui: &mut egui::Ui) {
+        ui.vertical_centered(|ui| {
+            ui.add(crate::egui_github_link_file!());
+        });
+
         let Self { text } = self;
 
         ui.horizontal(|ui| {

crates/egui_demo_lib/src/demo/window_with_panels.rs

@@ -67,6 +67,9 @@ impl super::View for WindowWithPanels {
                 ui.vertical_centered(|ui| {
                     ui.heading("Bottom Panel");
                 });
+                ui.vertical_centered(|ui| {
+                    ui.add(crate::egui_github_link_file!());
+                });
             });
 
         egui::CentralPanel::default().show_inside(ui, |ui| {