Add license headers

[cmarqu]

Please add license headers as requested in #1 (comment)
(Note that two different headers are used.)

[Ubermensch127]

Hi @cmarqu,

I’d like to work on this issue if it’s available.
I’ll follow the guidance from the referenced comment and make sure the two different license headers are applied correctly and consistently across the codebase.

Please let me know if there are any specific files or conventions you’d like me to prioritize.
Thanks!

[cmarqu]

Yes, feel free to open a pull request.
Basically, all files under copra/examples/ should be using

-- This file is public domain, it can be freely copied without restrictions.
-- SPDX-License-Identifier: CC0-1.0

and the rest should all be using

# Copyright cocotb contributors
# Licensed under the Revised BSD License, see LICENSE for details.
# SPDX-License-Identifier: BSD-3-Clause