Add missing license header

Author: Takishima

projectq/libs/qasm/_qiskit_conv.py

@@ -1,4 +1,17 @@
 # -*- coding: utf-8 -*-
+#   Copyright 2020 ProjectQ-Framework (www.projectq.ch)
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
 from projectq.ops import Barrier, H, S, Sdagger, T, Tdagger, X, Y, Z, Rx, Ry, Rz, Swap, Toffoli, C, CNOT, U2, U3
 
 # ==============================================================================