Add reference to cargo-unusued-features

Author: johnthagen

README.md

@@ -300,6 +300,8 @@ heuristic-based anti-virus software because malware often uses UPX.
 
 - [`cargo-bloat`](https://github.com/RazrFalcon/cargo-bloat) - Find out what takes most of the 
   space in your executable.
+- [`cargo-unused-features`](https://github.com/TimonPost/cargo-unused-features) - Find and prune
+  enabled, but, potentially unused feature flags from your project.
 - [`momo`](https://github.com/llogiq/momo) - `proc_macro` crate to help keeping the code footprint
   of generic methods in check.
 - [Twiggy](https://rustwasm.github.io/twiggy/index.html) - A code size profiler for Wasm.