Add rust version

Author: singpolyma

README

@@ -103,7 +103,8 @@ mndecode.c	Sample program - decode data from stdin to stdout
 
 == Other Implementations ==
 
-JavaScript: <https://github.com/mbrubeck/mnemonic.js>
+Elixr:      <https://github.com/mwmiller/mnemonex>
 Go:         <https://bitbucket.org/dchapes/mnemonicode>
+JavaScript: <https://github.com/mbrubeck/mnemonic.js>
 Python:     <https://github.com/bwhmather/python-mnemonicode>
-Elixr:      <https://github.com/mwmiller/mnemonex>
+Rust:       <https://github.com/mbrubeck/rust-mnemonic>