Fixes #1635. Fixed typo

doc/api/readline.markdown

@@ -9,7 +9,7 @@ to allow your program to gracefully terminate:
 
     var rl = require('readline');
 
-    var i = rl.createInterface(process.sdtin, process.stdout, null);
+    var i = rl.createInterface(process.stdin, process.stdout, null);
     i.question("What do you think of node.js?", function(answer) {
       // TODO: Log the answer in a database
       console.log("Thank you for your valuable feedback.");