Thanks for posting! You can add a text block to the invitation or registration form. I'm not sure which makes more sense for you but if it's something you want people to know when registering for your event I would recommend adding it to the registration form.
To add to the invite, edit the email and add any block (I recommend a greeting or content block) to your email. Delete any content that is in the block and add your disclaimer here.
To add it to the registration form you will want to be in the edit mode and click to add a text block.
Hope this helps!