docs: def add_signer(self, signer):
          """ Simple dict of {'name': 'John Doe', 'email': 'name@example.com'}"""
          if isinstance(signer, HelloSigner) and signer.validate():
              self.signers.append(signer)
          else:
              if not signer.validate():
                  raise Exception("HelloSigner Errors %s" % (signer.errors,))
              else:
                  raise Exception("add_signer signer must be an instance of class HelloSigner")