`look_at_point` user's guide assumes old implementation

Came up in !636 (merged).

The look_at_point functions were rewritten in 78f74b32. It appears as if view_direction has been replaced by obj_front, but the user's guide wasn't adapted to these changes. Running the examples results in

    look_at_point(arrow, point, bobj_front=(0, 0, 1))
  File "/var/home/flos/projects/pyddg/pyddg/ddg/visualization/blender/object.py", line 225, in look_at_point
    bobj_matrix_inv = np.linalg.inv(bobj_matrix)
  File "<__array_function__ internals>", line 180, in inv
  File "/var/home/flos/.cache/pypoetry/virtualenvs/pyddg-4YNAg0_4-py3.10/lib/python3.10/site-packages/numpy/linalg/linalg.py", line 545, in inv
    ainv = _umath_linalg.inv(a, signature=signature, extobj=extobj)
  File "/var/home/flos/.cache/pypoetry/virtualenvs/pyddg-4YNAg0_4-py3.10/lib/python3.10/site-packages/numpy/linalg/linalg.py", line 88, in _raise_linalgerror_singular
    raise LinAlgError("Singular matrix")
numpy.linalg.LinAlgError: Singular matrix

@tyburn, you're probably the most knowledgeable...