mention real msrv in readme

Author: Emilgardis

README.md

@@ -209,8 +209,7 @@ linker = "rust-lld"
 
 ## Minimum Supported Rust Version (MSRV)
 
-This crate is guaranteed to compile on stable Rust 1.64.0 and up. It *might*
-compile with older versions but that may change in any new patch release.
+This crate is guaranteed to compile on stable Rust 1.70.0 and up.
 
 ## License