Remove Rust documentation link

Removed Rust FFI documentation link from README.

Author: Batchhh

README.md

@@ -26,8 +26,6 @@ make check                            # verify exported symbols match specter.h
 
 [docs/usage.md](docs/usage.md) — C/C++ API reference and examples
 
-[docs/rust.md](docs/rust.md) — Using the library from Rust via FFI
-
 [docs/architecture.md](docs/architecture.md) — Internal design and data flows
 
 ## Contributing