use env_logger in all examples (#2934)

examples/file_dialog/src/main.rs

@@ -3,6 +3,7 @@
 use eframe::egui;
 
 fn main() -> Result<(), eframe::Error> {
+    env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
         drag_and_drop_support: true,
         initial_window_size: Some(egui::vec2(320.0, 240.0)),