add project maturity to README

README.md

@@ -48,6 +48,12 @@ To get started with the Stratum V2 Reference Implementation (SRI), please follow
 
 This guide provides all the necessary information on prerequisites, installation, and configuration to help you begin using, testing or contributing to SRI.
 
+## 🏅 Project Maturity
+
+Low-level crates (`protocols` directory) are considered **beta** software. Rust API Docs is a [work-in-progress](https://github.com/stratum-mining/stratum/issues/845), and the community should still expect small breaking API changes and patches.
+
+Application-level crates (`roles` directory) are considered **alpha** software, and bugs are expected. They should be used as a guide on how to consume the low-level crates as dependencies.
+
 ## 🚀 Use Cases
 
 The library is modular to address different use-cases and desired functionality. Examples include: