repl: add welcome message

[gengjiawen]

Motivation

I want to make node more friendly for new user. Actually it take me very long to find out node repl can load script :)

Also I am not quite sure I put the change in best location in repl.js.

Welcome message

The current welcome message is (copyed from windows powershell):

Welcome to Node.js v12.0.0-pre.
Type ".help" for more information.

Compare with other languages
In python (using docker run --rm -it python):

Python 3.7.2 (default, Jan 23 2019, 02:31:57) 
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.

In java (use docker run --rm -it openjdk:11):

Feb 05, 2019 2:42:25 PM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 11.0.1
|  For an introduction type: /help intro

May need port to Node 8 && 10.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines