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

deploytool/cmd/luci_deploy/deploy.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 (
         "sort"
 
         "github.com/luci/luci-go/common/cli"
@@ skipping 449 matching lines @@
 
                 // Container Engine Projects
                 for _, name := range reg.gkeProjectNames {
                         proj := reg.gkeProjects[name]
                         workC <- func() error {
                                 return proj.commit(w)
                         }
                 }
         })
 }