document in config.mak sample that x86_64 is supported
diff --git a/dist/config.mak b/dist/config.mak
index 5120552..452a93a 100644
--- a/dist/config.mak
+++ b/dist/config.mak
@@ -2,7 +2,7 @@
 # musl config.mak template (original in dist/config.mak)
 #
 
-# Target CPU architecture. Supported values: i386
+# Target CPU architecture. Supported values: i386, x86_64
 ARCH = i386
 
 # Installation prefix. DO NOT use /, /usr, or /usr/local !