Alternately, you can use this tool to generate one:
http://tools.trepmal.com/wp-readme-generator/

A readme.txt is needed so your plugin will display correctly in our repository, but also so we can make sure you're providing the users with all the information they need before they install your plugin. Our goal with this is to make sure everyone knows what they're installing and what they need to do before they install it. No surprises :)

This is especially important if your plugin is making calls back to your own servers. For the most part, we do not permit offloading of images or code, however in the case where you are providing a service (like Disqus or Akismet or Twitter), we permit it. The catch is you have to actually explain this to the layman in your readme, so they know where data is going.

Keep in mind, a readme.MD is not the same as a readme.TXT - the formatting for markup is different.

Please send a link so the completed plugin can be downloaded. Alternately you can reply to this and send a .zip or .rar file. As this is for a new plugin request, please reply within seven days of this email or we will reject your plugin.

1. Please place your $currency array into a function rather than leaving it as a global variable as you have it now.

2. All scripts should be loaded via wp_enqueue_script and placed inside of a function that is connected to the wp_enqueue_scripts action. For more information, refer to the codex page: http://codex.wordpress.org/Function_Reference/wp_enqueue_script

3. All settings saved with get/update_option need to be sanitized: http://codex.wordpress.org/Data_Validation

4. Please ensure that all $wpdb queries (both insert and select) are properly protected against SLQ injections: http://codex.wordpress.org/Class_Reference/wpdb#Protect_Queries_Against_SQL_Injection_Attacks

5. register_widget_control() has been deprecated, please update your widgets to use non-deprecated functions: https://codex.wordpress.org/Function_Reference/register_widget_control

5. register_sidebar_widget() has been deprecated, please update your widgets to use non-deprecated functions: https://codex.wordpress.org/Function_Reference/register_sidebar_widget

Once you have updated your plugin code, resubmit and we'll re-review it.