Small READMEs for -derive and -core

cmz-core/README.md

@@ -0,0 +1,5 @@
+`cmz-core` by Ian Goldberg, iang@uwaterloo.ca  
+Version 0.1.0-rc1, 2025-09-16
+
+This crate provides the core functionality for the macros in the
+[`cmz`](https://crates.io/crates/cmz) crate.

cmz-derive/README.md

@@ -0,0 +1,5 @@
+`cmz-derive` by Ian Goldberg, iang@uwaterloo.ca  
+Version 0.1.0-rc1, 2025-09-16
+
+This crate provides the derive macros for the
+[`cmz`](https://crates.io/crates/cmz) crate.