deploytool: Add README.md, migrate docs to it.

deploytool/cmd/luci_deploy/layout.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package main
 
 import (
         "io/ioutil"
         "os"
         "path/filepath"
@@ skipping 963 matching lines @@
                         return "", errors.Reason("could not find %(filename)q starting from %(dir)q").
                                 D("filename", filename).D("dir", dir).Err()
                 }
         }
 }
 
 type componentRegistrar interface {
         addGAEModule(*layoutDeploymentGAEModule)
         addGKEPod(*layoutDeploymentGKEPodBinding)
 }