Open the About popup the first time a new version starts

The last version the About popup was shown for is saved as last_seen_version in
settings.cfg. When the game starts with another version, About opens to show
what is new.

main/main_window.gd

@@ -43,6 +43,16 @@ func _ready() -> void:
 	statistics_view.soundtrack_selected.connect(soundtrack_stats_popup.show_soundtrack)
 
 	search_popup.get_list_of_soundtracks()
+	show_about_if_new_version()
+
+
+## Opens the About popup, with what is new, the first time this version starts.
+func show_about_if_new_version() -> void:
+	if Settings.last_seen_version == Settings.version:
+		return
+	Settings.last_seen_version = Settings.version
+	Settings.save_settings()
+	show_about()
 
 
 func _input(event: InputEvent) -> void: