Added comments for two branches in the instance detection

flask/app.py

@@ -575,8 +575,10 @@ class Flask(_PackageBoundObject):
             base_dir = py_prefix
         elif site_folder == 'site-packages':
             parent, folder = os.path.split(site_parent)
+            # Windows like installations
             if folder.lower() == 'lib':
                 base_dir = parent
+            # UNIX like installations
             elif os.path.basename(parent).lower() == 'lib':
                 base_dir = os.path.dirname(parent)
             else: