Add README and crypto/rand for encrypt.go tool (#1057)

node/hack/README.md

@@ -0,0 +1,3 @@
+This folder contains one-off cli tools to help with repair and discover operations.
+
+This code should not be imported by any other production tooling.

node/hack/encrypt/encrypt.go

@@ -1,11 +1,11 @@
 package main
 
 import (
+	"crypto/rand"
 	"encoding/base64"
 	"fmt"
 	"io"
 	"log"
-	"math/rand"
 	"os"
 
 	"github.com/certusone/wormhole/node/pkg/common"