chore: add license header

Signed-off-by: kwanhur <[email protected]>

CODE_OF_CONDUCT.md

@@ -1,3 +1,19 @@
+<!--
+  ~ Copyright 2022 kwanhur
+  ~
+  ~ 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.
+  ~
+-->
 
 *The following is copied for your convenience from <https://www.apache.org/foundation/policies/conduct.html>. If there's a discrepancy between the two, let us know or submit a PR to fix it.*