add MSRV policy section

README.md

@@ -11,6 +11,10 @@ Collection of [Message Authentication Code][1] (MAC) algorithms written in pure
 | [HMAC]    | `hmac` | [![crates.io](https://img.shields.io/crates/v/hmac.svg)](https://crates.io/crates/hmac) | [![Documentation](https://docs.rs/hmac/badge.svg)](https://docs.rs/hmac) | ![Minimum Supported Rust Version][msrv-1.41] |
 | [PMAC]    | `pmac` | [![crates.io](https://img.shields.io/crates/v/pmac.svg)](https://crates.io/crates/pmac) | [![Documentation](https://docs.rs/pmac/badge.svg)](https://docs.rs/pmac) | ![Minimum Supported Rust Version][msrv-1.41] |
 
+### Minimum Supported Rust Version (MSRV) Policy
+
+MSRV bumps are considered breaking changes and will be performed only with minor version bump.
+
 ## License
 
 All crates licensed under either of