Add missing README

Author: thejpster

cortex-ar-rt-macros/README.md

@@ -0,0 +1,28 @@
+# Macros for `cortex-a-rt` and `cortex-r-rt`
+
+This crate contains proc-macros that are re-exported through the following crates:
+
+* [`cortex-a-rt`]
+* [`cortex-r-rt`]
+
+[cortex-a-rt]: https://crates.io/crates/cortex-a-rt
+[cortex-r-rt]: https://crates.io/crates/cortex-r-rt
+
+## Minimum Supported Rust Version (MSRV)
+
+This crate is guaranteed to compile on stable Rust 1.82.0 and up. It *might*
+compile with older versions but that may change in any new patch release.
+
+## Licence
+
+* Copyright (c) Ferrous Systems
+* Copyright (c) The Rust Embedded Devices Working Group developers
+
+Licensed under either [MIT](./LICENSE-MIT) or [Apache-2.0](./LICENSE-APACHE) at
+your option.
+
+## Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in the work by you shall be licensed as above, without any
+additional terms or conditions.