For races or clubs using the RunSignUp website capability, you can easily add this as another Custom Section. From there, you can decide where it appears on your website – either on the Race/Club Info page or as part of a separate page or menu item. Note that you will need at least one email list created in Email Marketing before you see this option in the Custom Content.
To add the component, create a new customer section (Race -> Race Page -> Custom Content/Pages), and select Email Subscription as the Embed option:
Then select which Email Marketing List you want new subscribers added to:
If you are adding this form as a widget to your website, just create a new widget and select Email Subscription Form: