docs: def add_membership(self, email, role, **attrs):
          """
          Add a Membership to the project and returns a
          :class:`Membership` resource.
  
          :param email: email for :class:`Membership`
          :param role: role for :class:`Membership`
          :param attrs: role for :class:`Membership`
          :param attrs: optional :class:`Membership` attributes
          """
          return Memberships(self.requester).create(
              self.id, email, role, **attrs
          )