Update MSRV policy

README.md

@@ -13,9 +13,18 @@ Documentation:
 
 ## Minimum Rust version policy
 
-The time crate is guaranteed to compile with any release of rustc from the past six months.
-Optional feature flags that enable interoperability with third-party crates (e.g. rand)
-follow the policy of that crate if stricter.
+`time` is guaranteed to compile with the latest stable release of Rust in addition to the two prior
+minor releases. For example, if the latest stable Rust release is 1.70, then `time` is guaranteed to
+compile with Rust 1.68, 1.69, and 1.70.
+
+The minimum supported Rust version may be increased to one of the aforementioned versions if doing
+so provides the end user a benefit. However, the minimum supported Rust version may also be bumped
+to a version four minor releases prior to the most recent stable release if doing so improves code
+quality or maintainability.
+
+For interoperability with third-party crates, it is guaranteed that there exists a version of that
+crate that supports the minimum supported Rust version of `time`. This does not mean that the latest
+version of the third-party crate supports the minimum supported Rust version of `time`.
 
 ## Contributing