better unsupported error message

Author: pickfire

rustup-init.sh

@@ -442,7 +442,7 @@ downloader() {
         if [ -n "$_err" ]; then
             echo "$_err" >&2
             if echo "$_err" | grep -q 'ERROR 404: Not Found\.$'; then
-                err "unsupported platform $3"
+                err "installer for platform '$3' not found, this may be unsupported"
             fi
         fi
         return $_status