Add an official MSRV policy

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
     strategy:
       matrix:
         # When updating this, the reminder to update the minimum supported
-        # Rust version in Cargo.toml.
+        # Rust version in Cargo.toml and README.md.
         rust: ['1.47']
     steps:
       - uses: actions/checkout@v3

README.md

@@ -99,6 +99,10 @@ Another useful tool for making certificates is [mkcert].
 
 [mkcert]: https://github.com/FiloSottile/mkcert
 
+## MSRV Policy
+
+The Minimum Supported Rust Version (MSRV) of this crate is **1.47.0**. As a **tentative** policy, the MSRV will not advance past the [current Rust version provided by Debian Stable](https://packages.debian.org/stable/rust/rustc). At the time of writing, this version of Rust is *1.48.0*. However, the MSRV may be advanced further in the event of a major ecosystem shift or a security vulnerability.
+
 ## License
 
 Licensed under either of