Note triples in README

README.md

@@ -8,3 +8,17 @@ various systems, including libc.
 [![Build status](https://ci.appveyor.com/api/projects/status/v0414slj8y8nga0p?svg=true)](https://ci.appveyor.com/project/alexcrichton/libc)
 
 [Documentation](http://alexcrichton.com/libc)
+
+## Platform Support
+
+Tested:
+  * `{i686,x86_64}-pc-windows-{msvc,gnu}`
+  *  `{i686,x86_64,mips,aarch64}-unknown-linux-gnu`
+  *  `x86_64-unknown-linux-musl`
+  *  `arm-unknown-linux-gnueabihf`
+  *  `arm-linux-androideabi`
+  *  `{i686,x86_64}-apple-darwin`
+
+Untested:
+  * `{i686,x86_64}-unknown-freebsd`
+  * `x86_64-unknown-{bitrig,dragonfly,openbsd,netbsd}`