README: Add few hints on usage/requirements.

Author: Paul Sokolovsky

README.md

@@ -3,3 +3,7 @@ WebREPL client for MicroPython
 
 This repository contains the WebREPL client and related tools, for
 accessing a MicroPython REPL over WebSockets.
+
+To start WebREPL terminal client, clone or download this repository
+(in full) and open webrepl.html in a browser. Recent versions of
+Firefox and Chrome (or Chromium) are supported.