fetch: remove experimental note

README.md

@@ -178,10 +178,6 @@ Implements [fetch](https://fetch.spec.whatwg.org/#fetch-method).
 
 Only supported on Node 16.8+.
 
-This is [experimental](https://nodejs.org/api/documentation.html#documentation_stability_index) and is not yet fully compliant with the Fetch Standard.
-We plan to ship breaking changes to this feature until it is out of experimental.
-Help us improve the test coverage by following instructions at [nodejs/undici/#951](https://github.com/nodejs/undici/issues/951).
-
 Basic usage example:
 
 ```js