get $CGB_BOOTROM/$DMG_BOOTROM from env

gb-emu/src/main.rs

@@ -23,7 +23,7 @@ mod camera;
 mod debug;
 mod window;
 
-/// Gameboy (DMG-A/B/C) emulator
+/// Gameboy (DMG/CGB) emulator
 #[derive(Parser, Debug)]
 #[command(author, version, about, long_about = None)]
 #[command(group(ArgGroup::new("saves").args(["save","no_save"])))]
@@ -128,7 +128,16 @@ impl EmulatorHandler {
             } else {
                 SerialTarget::None
             })
-            .with_bootrom(args.bootrom.map(RomFile::Path), args.show_bootrom)
+            .with_bootrom(
+                args.bootrom
+                    .or(if args.dmg {
+                        std::env::var("DMG_BOOTROM").ok()
+                    } else {
+                        std::env::var("CGB_BOOTROM").ok()
+                    })
+                    .map(RomFile::Path),
+                args.show_bootrom,
+            )
             .with_no_save(args.no_save)
             .with_tile_window(tile_window)
             .with_cgb_mode(!args.dmg);