Add a comment for config.mk saying we build all archs by default
diff --git a/config.mk b/config.mk
index 3b27ec3..1ab2da0 100644
--- a/config.mk
+++ b/config.mk
@@ -1,5 +1,5 @@
 ################################################################################
-# Specify which archs you want to compile in.
+# Specify which archs you want to compile in. By default, we build all archs.
 # DO NOT touch the line below.
 CAPSTONE_ARCHS =