README: improve description of Rust

Author: tshepang

README.md

@@ -1,12 +1,14 @@
 # The Rust Programming Language
 
-Rust is a systems programming language that is fast, memory safe and
-multithreaded, but does not employ a garbage collector or otherwise
-impose significant runtime overhead.
+Rust is a fast systems programming language that guarantees
+memory safety and offers painless concurrency ([no data races]).
+It does not employ a garbage collector and has minimal runtime overhead.
 
 This repo contains the code for `rustc`, the Rust compiler, as well
 as standard libraries, tools and documentation for Rust.
 
+[no data races]: http://blog.rust-lang.org/2015/04/10/Fearless-Concurrency.html
+
 ## Quick Start
 
 Read ["Installing Rust"] from [The Book].