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

deploytool/cmd/luci_deploy/deploy_appengine.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 (
         "fmt"
         "path/filepath"
         "sort"
@@ skipping 790 matching lines @@
 
                         default:
                                 return nil, errors.Reason("unknown task queue type %(type)T").D("type", t).Err()
                         }
 
                         queueYAML.Queue = append(queueYAML.Queue, &entry)
                 }
         }
         return &queueYAML, nil
 }