[DOC] Update ZJIT status in NEWS.md

As for Ruby v4.0.0-preview3, ZJIT support is enabled by default on
supported platforms. The previous phrasing is not relevant for most
users. Replaced with brief instructions for enabling the JIT itself.

Author: chancancode

NEWS.md

@@ -510,7 +510,7 @@ A lot of work has gone into making Ractors more stable, performant, and usable.
 
 * ZJIT
     * Introduce an [experimental method-based JIT compiler](https://docs.ruby-lang.org/en/master/jit/zjit_md.html).
-      To enable `--zjit` support, build Ruby with Rust 1.85.0 or later.
+      To enable ZJIT on supported platforms, supply the `--zjit` option or call `RubyVM::ZJIT.enable` at runtime.
     * As of Ruby 4.0.0, ZJIT is faster than the interpreter, but not yet as fast as YJIT.
       We encourage experimentation with ZJIT, but advise against deploying it in production for now.
     * Our goal is to make ZJIT faster than YJIT and production-ready in Ruby 4.1.