fix #683 add upgrade tip to readme (#686)

LICENSE

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2017~end of time      electerm, ZHAO Xudong <zxdong@gmail.com>
+Copyright (c) 2017~tomorrow      electerm, ZHAO Xudong <zxdong@gmail.com>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -22,7 +22,7 @@
 
 ## dowload
 - https://electerm.html5beta.com
-- https://github.com/electerm/electerm/releases
+- or from release: https://github.com/electerm/electerm/releases
 
 ## or install from npm
 ```
@@ -33,6 +33,11 @@ npm i -g electerm
 
 ```
 
+## upgrade
+
+- if you downloaded it, then just download the latest edition, reinstall.
+- if you install from npm, just run `npm i -g electerm` again.
+
 ## features
 - work as a terminal/file manager or ssh/sftp client(similar to xshell)
 - global hotkey to toggle window visibility (simliar to guake, default is `ctrl + 2`)