Update setup.py

setup.py

 import setuptools
-import CpicImgSim
+import csst_cpic_sim
 
 setuptools.setup(
     name='csst_cpic_sim',
-    version=CpicImgSim.__version__,
+    version=csst_cpic_sim.__version__,
     author='CSST Team',
     author_email='gzhao@niaot.ac.cn',
     description='The CSST CPIC Simulation',  # short description