add crate level documentation
+//! A test harness for embedded devices
+//!
+//! This crate has a single API: the `#[tests]` macro. This macro is documented in the project
+//! README which can be found at:
+//!
+//! - https://crates.io/crates/defmt (crates.io version)
+//! - https://github.com/knurling-rs/defmt/tree/main/firmware/defmt-test (git version)
+
#![no_std]
pub use defmt_test_macros::tests;
