We currently do not have the W-8BEN-E tax form as an option on the site so you will need to fill out the form and email to firstname.lastname@example.org.
When you make a withdrawal you will need to notify us so we can manually attach your tax form to your withdrawal.
Official instructions: https://www.irs.gov/pub/irs-pdf/iw8bene.pdf
Some helpful instructions: http://www.plantemoran.com/services/tax/documents/doing-business-with-foreign-entities.pdf
You need # 1,2,3,4,5,6,7 filled out and a signature in part XXIX at a minimum.