Update README
Update README

- Fixed some spelling/grammar issues
- Added new pictures/gifs or replaced old ones to reflect the current state of the importer better
- Added a section for how to use ArticyRef, given that it is now the default accessor for objects.

- Images are hosted on gyazo right now, should be hosted on articy web server
ArticySoftware/ArticyImporterForUnreal,ArticySoftware/ArticyImporterForUnreal,ArticySoftware/ArticyImporterForUnreal