Update instructions with latest Rustc version tested

Author: rsaarelm

README.md

@@ -3,11 +3,13 @@ PHAGE -- 2015 7DRL roguelike
 Build instructions
 ------------------
 
-Phage should build with the Rust language compiler version 1.0.0.
+Phage should build with a stable 1.x version of the Rust compiler. It was last
+tested with version 1.13. You need to install the Rust programming language,
+either from [the Rust website](https://www.rust-lang.org/en-US/downloads.html)
+or from the package manager of your operating system.
 
-If you're on Windows, you will also need to have MinGW GCC installed
-and in your command line path to be able to build the third-party
-dependencies.
+If you're on Windows, you will also need to have MinGW GCC installed and in
+your command line path to be able to build the third-party dependencies.
 
 With rustc in your path, just go to the Phage directory and type