update gitignore

Former-commit-id: 7dbce9970b12d76cab3515e6b154e8fa8da6dbc6

.gitignore

@@ -75,3 +75,6 @@ optional/build
 lib
 tutorial/XXX_test/CMakeLists.txt
 tutorial/XXX_test/main.cpp
+python/py_igl/todo
+python/build
+python/.idea