Missing `NOTICE` file in source distribution

[Fokko]

Hey all,

Just a reminder that every ASF source distribution must include a notice file: https://www.apache.org/legal/src-headers.html#notice It seems to be missing from this project.

[jbonofre]

Thanks. Let me check here.

[kou]

Oh, sorry. I missed it.

I also noticed that LICENSE is just a license header not the full Apache 2.0 license content.

I opened #545 for them.