fix cpic source error

.. toctree::

   :maxdepth: 1

   目标仿真模块 </notebooks/1_target_example.ipynb>

   焦面模块 </notebooks/2_focus_example.ipynb>

   观测效应仿真模块 </notebooks/3_obs_effect.ipynb>

   相机仿真模块 </notebooks/4_camera_example.ipynb>

   点扩散函数仿真模块 </notebooks/5_psf_example.ipynb>

   目标仿真模块 </source/cpic/notebooks/1_target_example.ipynb>

   焦面模块 </source/cpic/notebooks/2_focus_example.ipynb>

   观测效应仿真模块 </source/cpic/notebooks/3_obs_effect.ipynb>

   相机仿真模块 </source/cpic/notebooks/4_camera_example.ipynb>

   点扩散函数仿真模块 </source/cpic/notebooks/5_psf_example.ipynb>