[Doc] Update notice

README.md

@@ -14,9 +14,11 @@ Alba is a JSON serializer for Ruby, JRuby, and TruffleRuby.
 ## IMPORTANT NOTICE
 
 Both version `3.0.0` and `2.4.2` contain important bug fix.
-However, version `3.0.0` has some bugs (see https://github.com/okuramasafumi/alba/issues/342).
+~~However, version `3.0.0` has some bugs (see https://github.com/okuramasafumi/alba/issues/342).
 Until they get fixed, it's highly recommended to upgrade to version `2.4.2`.
-Dependabot and similar tools might create an automated Pull Request to upgrade to `3.0.0`, so it might be required to upgrade to `2.4.2` manually.
+Dependabot and similar tools might create an automated Pull Request to upgrade to `3.0.0`, so it might be required to upgrade to `2.4.2` manually.~~
+Version `3.0.1` has been released so Ruby 3 users should upgrade to `3.0.1`.
+For Ruby 2 users, it's highly recommended to upgrade to `2.4.2`.
 Sorry for the inconvenience.
 
 ## TL;DR