WordPress.org

1. Upload whole wp-posturl directory to the /wp-content/plugins/ directory;
2. Activate the plugin through the 'Plugins' menu in WordPress;
3. Goto "Setting --> Add Post URL" page to define your user specific text and other options. The default setting is suitable for most of usage;
4. When you new a post or edit a post, you can change "Add Post URL?" option in the editor to decide whehter or not adding the header/footer text for this post.

Your original configuration will be totally kept during upgrading. But please backup before upgrading to avoid configuration lost.

You can completely uninstall WP-PostURL plugin. It will remove all the option settings created by this plugin, and deactive this plugin at the same time.