[LICENSE] Add hidden SPDX headers to markdown files

qflow/README

diff --git a/qflow/README b/qflow/README
index f58340e..0871548 100644
--- a/qflow/README
+++ b/qflow/README
@@ -1,3 +1,21 @@
+<!---
+# SPDX-FileCopyrightText: 2020 Efabless Corporation
+#
+# 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.
+#
+# SPDX-License-Identifier: Apache-2.0
+-->
+
 The qflow directory entries are only used to verify the all-digital frequency
 locked loop circuit by running the verilog modules ring_osc2x13 and
 digital_pll_controller seperately through synthesis.