use env_logger in all examples (#2934)

examples/custom_3d_glow/Cargo.toml

@@ -13,4 +13,5 @@ eframe = { path = "../../crates/eframe", features = [
     "__screenshot", # __screenshot is so we can dump a screenshot using EFRAME_SCREENSHOT_TO
 ] }
 egui_glow = { path = "../../crates/egui_glow" }
+env_logger = "0.10"
 glow = "0.12"

examples/custom_3d_glow/src/main.rs

@@ -7,6 +7,7 @@ use egui::mutex::Mutex;
 use std::sync::Arc;
 
 fn main() -> Result<(), eframe::Error> {
+    env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
     let options = eframe::NativeOptions {
         initial_window_size: Some(egui::vec2(350.0, 380.0)),
         multisampling: 4,