I get error readline() function

Is the output you shared from before or after you installed readline? In any case, based on the error message you've shared, it looks like your system doesn't have readline installed, or it isn't available to your app for some reason. That line of code prompts the user to enter the authorization code they receive from the Dropbox Web site.

That means you just need to install readline (or debug why it's not available to your app) or replace readline with whatever function is available on your platform for accepting input from the user, though that may be specific to your platform so I can't say off hand what the right answer for your system is. For example, here's a post about this for Ubuntu:

http://askubuntu.com/questions/182989/how-to-solve-fatal-error-call-to-undefined-function-readline-readline-librar