How exactly can I add a mantle token to my cryptocurrency portfolio? I'm a bit new to this field and would appreciate a step-by-step guide. Could you please elaborate on the necessary steps, including any prerequisites or requirements I might need to fulfill? Also, is there a specific platform or exchange where I can find and add mantle tokens? Additionally, could you share any tips or advice on managing and storing these tokens securely? Thank you for your assistance in this matter.