Add note that Ruby 2.8 support is experimental [ci skip] [doc]

CHANGELOG.md

@@ -13,7 +13,7 @@
 * [#31](https://github.com/rubocop-hq/rubocop-ast/pull/31): NodePattern now uses `param === node` to match params, which allows Regexp, Proc, Set in addition to Nodes and literals. ([@marcandre][])
 * [#41](https://github.com/rubocop-hq/rubocop-ast/pull/41): Add `delimiters` and related predicates for `RegexpNode`. ([@owst][])
 * [#46](https://github.com/rubocop-hq/rubocop-ast/pull/46): Basic support for [non-legacy AST output from parser](https://github.com/whitequark/parser/#usage). Note that there is no support (yet) in main RuboCop gem. ([@marcandre][])
-* [#48](https://github.com/rubocop-hq/rubocop-ast/pull/48): Support `Parser::Ruby28` for Ruby 2.8 (3.0) parser. ([@koic][])
+* [#48](https://github.com/rubocop-hq/rubocop-ast/pull/48): Support `Parser::Ruby28` for Ruby 2.8 (3.0) parser (experimental). ([@koic][])
 * [#35](https://github.com/rubocop-hq/rubocop-ast/pull/35): NodePattern now accepts `%named_param` and `%CONST`. The macros `def_node_pattern` and `def_node_search` accept default named parameters. ([@marcandre][])
 
 ## 0.0.3 (2020-05-15)