The WakaTime Gedit plugin is open-source on GitHub.
Download the latest plugin release from GitHub.
Run the install.py script as root.
Edit ~/.wakatime.cfg and add your apikey as follows:
api_key = <your-api-key>
Activate the plugin in Gedit from Edit → Preferences → Plugins.
Use Gedit like you normally do, WakaTime will run in the background.
Visit https://wakatime.com/dashboard to see your coding activity.