list features in docs, that jumped over ES5.1 (ES6)

Class has been implemented at https://github.com/dop251/goja/commit/0b5d2105245750c4ba3305bf31081f36fdca9862. It is great feature, thank you.

At this time, static/private was also implemented. this goes beyond ES6. People who come later, may missed this feature(even it's a great feature.).

Do you plan to list features that jumped over ES5.1 (ES6) in the Readme? or is it ok to contribute to the Readme?