add a setup document, and tweak the scripts that it mentions

SVN=122175

src/cmd/clean.bash

@@ -3,7 +3,6 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-
 for i in 6l 6a 6c 6g gc cc
 do
 	cd $i

src/make.bash

+#!/bin/bash
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+for i in cmd runtime
+do
+	cd $i
+	bash make.bash
+	cd ..
+done