add .gitignore and rm .DS_Store

.gitignore

@@ -0,0 +1,30 @@
+# compilation and distribution
+__pycache__
+_ext
+*.pyc
+*.so
+detectron2.egg-info/
+build/
+dist/
+wheels/
+
+# pytorch/python/numpy formats
+*.pth
+*.pkl
+*.npy
+
+# ipython/jupyter notebooks
+*.ipynb
+**/.ipynb_checkpoints/
+
+# Editor temporaries
+*.swn
+*.swo
+*.swp
+*~
+
+# editor settings
+.idea
+.vscode
+
+.DS_Store