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

deploytool/cmd/config.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 (
-        "path/filepath"
-
-        "github.com/luci/luci-go/common/errors"
-        log "github.com/luci/luci-go/common/logging"
-        "github.com/luci/luci-go/deploytool/api/deploy"
-
-        "github.com/mitchellh/go-homedir"
-        "golang.org/x/net/context"
-)
-
-const userCfgName = ".luci_deploytool"
-
-func loadUserConfig(c context.Context, cfg *deploy.UserConfig) error {
-        path, err := homedir.Dir()
-        if err != nil {
-                log.WithError(err).Warningf(c, "Failed to get user home directory; cannot load local config.")
-                return nil
-        }
-
-        configPath := filepath.Join(path, userCfgName)
-        switch err := unmarshalTextProtobuf(configPath, cfg); {
-        case err == nil:
-                log.Infof(c, "Loaded user config from: %s", configPath)
-
-        case isNotExist(err):
-                log.Debugf(c, "No user config found at: %s", configPath)
-
-        default:
-                return errors.Annotate(err).Reason("failed to load config at [%(path)s]").D("path", configPath).Err()
-        }
-
-        return nil
-}