docs(test2): Cover macro return type differences

Author: epage

crates/libtest2/src/lib.rs

@@ -35,6 +35,8 @@
 //!
 //! Some of the notable differences:
 //!
+//! - `#[test]` does not support all `Termination` types as return values,
+//!   only what [`IntoRunResult`] supports.
 //! - Output capture and `--no-capture`: simply not supported. The official
 //!   `libtest` uses internal `std` functions to temporarily redirect output.
 //!   `libtest` cannot use those, see also [libtest2#12](https://github.com/assert-rs/libtest2/issues/12)