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

deploytool/cmd/luci_deploy/tools.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 (
         "os"
         "os/exec"
         "path/filepath"
@@ skipping 200 matching lines @@
 }
 
 type gcloudTool struct {
         exe     string
         project string
 }
 
 func (t *gcloudTool) exec(command string, args ...string) *workExecutor {
         return execute(t.exe, append([]string{"--project", t.project, command}, args...)...)
 }