let's add copyrights checker to CI pipeline

[yegor256]

See, how it's done here: https:/objectionary/eo/blob/master/.github/workflows/copyrights.yml

[yegor256]

@deemp please, consider this

[deemp]

@yegor256, please write:

• motivation for this proposal
• list of regexes for file names that we should check

[yegor256]

@deemp it's mostly a matter of discipline. If every file has a copyright notice in front of it, this will guarantee that when this particular file is found somewhere outside of this repository, it will be clear who created it and who can use/copy it. I suggest checking all text files, including .yaml, .hs, and every other format you can annotate with a license.

[deemp]

@yegor256, which license should we use?

[yegor256]

@deemp use the one I added to the root directory: https:/objectionary/normalizer/blob/master/LICENSE.txt