def add_observee(self, observee_id):
response = self._requester.request(<EOL>'<STR_LIT>',<EOL>'<STR_LIT>'.format(self.id, observee_id)<EOL>)<EOL>return User(self._requester, response.json())<EOL>
Registers a user as being observed by the given user.

:calls: `PUT /api/v1/users/:user_id/observees/:observee_id \
<https://canvas.instructure.com/doc/api/user_observees.html#method.user_observees.update>`_

:param observee_id: The login id for the user to observe.
:type observee_id: int
:rtype: :class: `canvasapi.user.User`