Add readme for node.js demos

Author: linev

demo/node/Readme.md

@@ -0,0 +1,19 @@
+# Use of JSROOT with Node.js
+
+JSROOT is provided as npm module and always can be installed as:
+
+    npm install jsroot
+
+After this JSROOT functionality can be used from Node.js scripts via:
+
+    var jsroot = require("jsroot");
+
+Main motivation to use JSROOT from Node.js is creation of SVG files.
+Example <makesvg.js> you will find in this directory. Just call it:
+
+    node makesvg.js
+
+JSROOT also provides possibility to read arbitrary TTree data without involving 
+any peace of native ROOT code. <tree.js> demonstrate such example:
+
+    node tree.js