docs: document deprecation

Author: 0xteddybear

README.md

@@ -10,6 +10,19 @@
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+## Soft-deprecation notice
+
+Smock has had a fruitful life, and its legacy lives on
+[smock-foundry](https://github.com/defi-wonderland/smock-foundry), a
+re-implementation for foundry which we now use exclusively as a side-effect of
+using `foundry` for all new projects.
+
+This project will receive security/bug fixes and code review for the
+foreseeable future, so existing projects can continue to use it, but no further
+features will be implemented. In particular, we won't migrate the project to
+newer versions of peer dependencies, as specified in
+[#201](https://github.com/defi-wonderland/smock/issues/201)
+
 **Smock** is the **S**olidity **mock**ing library. It's a plugin for
 [hardhat](https://hardhat.org) that can be used to create mock Solidity
 contracts entirely in JavaScript (or TypeScript!). With Smock, it's