Add pkl to GitHub linguist

[1cedsoda]

GitHub Linguist can detect the language of a file based on different methods. It is related to syntax highlighting on GitHub and to generate language statistics inside GitHub repos:

I think it's a problem, that there already is another format called pickle with the file extension .pkl. Its Python related.

Would be great to add pkl grammar to linguist as it improves code readability on GitHub.

Linguist has quantitative requirements of how many public files of a specific language are hosted on GitHub, before they consider adding it, which might have not been reached yet.