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

deploytool/cmd/luci_deploy/version_test.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 (
         "testing"
 
         "github.com/luci/luci-go/deploytool/api/deploy"
@@ skipping 43 matching lines @@
 
                         s := v.String()
                         So(s, ShouldEqual, "__minor-major-tainted-test_person")
 
                         parsed, err := parseCloudProjectVersion(deploy.Deployment_CloudProject_DEFAULT, s)
                         So(err, ShouldBeNil)
                         So(parsed, ShouldResemble, v)
                 })
         })
 }