Add an operation to this Run instance.

        :Parameters:
          - `original_index`: The original index of this operation
            within a larger bulk operation.
          - `operation`: The operation document.

def add(self, original_index, operation):
        """Add an operation to this Run instance.

        :Parameters:
          - `original_index`: The original index of this operation
            within a larger bulk operation.
          - `operation`: The operation document.
        """
        self.index_map.append(original_index)
        self.ops.append(operation)