Edit to acrissCode to note it's European only

Hi all,

If we're going to keep acrissCode as a fundamental property of Car
<https://schema.org/Car>, I think we should make clear that it only applies
to European car rentals. The current text reads:

​​The ACRISS Car Classification Code is a code used by many car rental
> companies, for classifying vehicles. ACRISS stands for Association of Car
> Rental Industry Systems and Standards.


​I propose the following edit:

​
> ​
> The ACRISS Car Classification Code is used by many European car rental
> companies for classifying vehicles. ACRISS stands for Association of Car
> Rental Industry Systems and Standards, a European industry group.


(Note that I also deleted "is a code" since it seemed obvious and redundant
immediately following "Car Classification Code...")

Source: http://www.acriss.org/who-is-acriss/

I can't see on Github where to do a PR on this text. Is it data/releases?
What is an .nt file?

Cheers,

JD