Partially documented the readline module.

doc/api/readline.markdown

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+## Readline
+
+This module allows reading of a stream (such as STDIN) on a line-by-line basis.
+
+Note that once you've invoked this module, your node program will not terminate
+until you've closed the interface, and the STDIN stream. Here's how to allow
+your program to gracefully terminate:
+
+<pre>
+var readline = require('readline');
+
+var i = readline.createInterface(process.sdtin, 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.");
+  i.close();                //These two lines together allow the program to
+  process.stdin.destroy();  //terminate. Without them, it would run forever.
+});
+</pre>
+
+### createInterface(input, output, completer)
+
+Returns an interface object, which reads from input, and writes to output.
+TODO: I think "completer" is used for tab-completion, but not sure.
+
+### interface.setPrompt(prompt, length)
+
+TODO
+
+### interface.prompt()
+
+TODO: Appears to trigger showing the prompt.
+
+### interface.question(query, cb)
+
+Displays the query to the user, and then calls the callback after the user
+has typed in their response.
+
+Example usage:
+
+<pre>
+interface.question("What is your favorite food?", function(answer) {
+  console.log("Oh, so your favorite food is " + answer);
+});
+</pre>
+
+### interface.close()
+
+TODO
+
+### interface.pause()
+
+TODO
+
+### interface.resume()
+
+TODO
+
+### interface.write()
+
+TODO