Add Claro Syntax Highlighting to "GitHub Linguist"

[JasonSteving99]

Apparently GitHub implements its syntax highlighting based on rules in this file https://github.com/github/linguist/blob/master/lib/linguist/languages.yml

In order for .claro files to start getting properly syntax highlighted, I'd need to get a pull request approved on that repo....that's probably not going to happen for quite some time, particularly until Claro's syntax is much more stable and more importantly Claro is not so much a "toy language". So I'll consider this a finish line goal for a few years from now :).