When exporting your JAR, in the "Select the resources to export" panel, you need to put a checkmark next to "config.properties".
Then, you'll need to change the way you load the properties file:
BufferedReader br = new BufferedReader(new InputStreamReader(getClass().getResourceAsStream("/config.properties")));
Also properties files usually aren't read that way -- try Properties.load:
Properties props = new Properties();
props.load(PropsSaver.class.getResourceAsStream("/config.properties"));