docs: add weld psa to readme (#2206)

Author: danceratopz

README.md

@@ -8,6 +8,8 @@
 
 The full execution-spec-tests documentation can be found [here](https://eest.ethereum.org/main/).
 
+**Note:** All of [ethereum/execution-spec-tests](https://github.com/ethereum/execution-spec-tests) functionality (i.e., the spec tests, test frameworks and tooling) will move to [ethereum/execution-specs](https://github.com/ethereum/execution-specs) in Q4 2025 to streamline spec and test development. For more information please see our [blog post](https://steel.ethereum.foundation/blog/blog_posts/2025-09-11_weld-announcement/). For now, please continue contributing to both [ethereum/execution-spec-tests](https://github.com/ethereum/execution-spec-tests) and [ethereum/execution-specs](https://github.com/ethereum/execution-specs) as you previously have - we will reach out to you if and when need be!
+
 [ethereum/execution-spec-tests](https://github.com/ethereum/execution-spec-tests) is both a collection of test cases and a framework implemented in Python to generate tests for Ethereum execution clients.
 
 The framework collects and executes the test cases in order to generate _test fixtures_ (JSON) which can be consumed by any execution client to verify their implementation of [ethereum/execution-specs](https://github.com/ethereum/execution-specs). The fixtures, which define state transition and block tests, are generated by the framework using one of the `t8n` command-line tools that are provided by most execution clients, see below for an overview of the supported `t8n` tools.