Download the latest release. It would be named stellate-<version>.zip. Extract it.
Inside the extracted folder there would be stellate.exe. Copy it, and then press Win+R keys and type shell:startup. Upon hitting enter a folder will open up. Right click and choose Paste Shortcut.
Double-click on this shortcut. The program will run.
Use Pause key to increase and Scroll Lock key to decrease brightness.
You can close Stellate from system tray.
The program will automatically run whenever you would restart Windows. If you don't want that you can delete that shortcut you pasted.
How to Build and Use
Clone this repository
Install golang
Run go build -ldflags "-H=windowsgui" in the project root (this may take few mins to complete). A file called stellate.exe will be built.
You can double-click on it to run it and close it from the system tray