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

deploytool/cmd/luci_deploy/util.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 (
         "go/build"
         "io/ioutil"
         "os"
@@ skipping 106 matching lines @@
 
 func findGoPackage(pkg string, goPath []string) string {
         bctx := build.Default
         bctx.GOPATH = strings.Join(goPath, string(os.PathListSeparator))
         p, err := bctx.Import(pkg, "", build.FindOnly)
         if err != nil {
                 return ""
         }
         return p.Dir
 }