Alphabetize Tier 1 supported platforms

Author: Susurrus

README.md

@@ -50,20 +50,20 @@ The following targets are all supported by nix on Rust 1.13.0 or newer (unless
 otherwise noted):
 
 Tier 1:
-  * i686-unknown-linux-gnu
-  * x86_64-unknown-linux-gnu
-  * i686-apple-darwin
-  * x86_64-apple-darwin
   * aarch64-unknown-linux-gnu
-  * armv7-unknown-linux-gnueabihf
   * arm-unknown-linux-gnueabi
-  * x86_64-unknown-freebsd
+  * armv7-unknown-linux-gnueabihf
+  * i686-apple-darwin
+  * i686-unknown-linux-gnu
+  * i686-unknown-linux-musl
+  * mips-unknown-linux-gnu
+  * mipsel-unknown-linux-gnu
   * powerpc-unknown-linux-gnu
   * powerpc64-unknown-linux-gnu
   * powerpc64le-unknown-linux-gnu
-  * mips-unknown-linux-gnu
-  * mipsel-unknown-linux-gnu
-  * i686-unknown-linux-musl
+  * x86_64-apple-darwin
+  * x86_64-unknown-freebsd
+  * x86_64-unknown-linux-gnu
   * x86_64-unknown-linux-musl
 
 Tier 2: