[Fix] Catch symlink failure on Windows (#1096)

setup.py

 from setuptools import find_packages, setup
 
 import os
+import platform
 import shutil
 import sys
 import torch
@@ -150,7 +151,11 @@ def add_mim_extention():
     # parse installment mode
     if 'develop' in sys.argv:
         # installed by `pip install -e .`
-        mode = 'symlink'
+        if platform.system() == 'Windows':
+            # set `copy` mode here since symlink fails on Windows.
+            mode = 'copy'
+        else:
+            mode = 'symlink'
     elif 'sdist' in sys.argv or 'bdist_wheel' in sys.argv:
         # installed by `pip install .`
         # or create source distribution by `python setup.py sdist`