Update doc url

Author: alexcrichton

README.md

@@ -3,7 +3,7 @@
 [![Build Status](https://travis-ci.org/alexcrichton/stacker.svg?branch=master)](https://travis-ci.org/alexcrichton/stacker)
 [![Build status](https://ci.appveyor.com/api/projects/status/1yca9gp2bhe9h2by?svg=true)](https://ci.appveyor.com/project/alexcrichton/stacker)
 
-[Documentation](http://alexcrichton.com/stacker)
+[Documentation](https://docs.rs/stacker)
 
 A stack-growth library for Rust. Enables annotating fixed points in programs
 where the stack may want to grow larger. Spills over to the heap if the stack