Document the current state of the project in the readme (#1069)

Author: Earlopain

README.md

@@ -13,6 +13,11 @@ equivalent source code from Parser's ASTs.
 Sponsored by [Evil Martians](http://evilmartians.com).
 MacRuby and RubyMotion support sponsored by [CodeClimate](http://codeclimate.com).
 
+> [!WARNING]  
+> The `parser` gem is only compatible with the syntax of Ruby 3.3 and lower. For Ruby 3.4 and later, please use the [`Prism::Translation::Parser`](https://github.com/ruby/prism/blob/main/docs/parser_translation.md) instead.
+> Starting in Ruby 3.4, Prism is the parser used in Ruby itself and can produce AST that is identical to the output of the `parser` gem. If you only need to parse Ruby 3.3 (or greater) and don't require compatibility with the `parser` gem AST, also consider using the native Prism AST.
+> See this [GitHub issue](https://github.com/whitequark/parser/issues/1046) for more details.
+
 ## Installation
 
     $ gem install parser