Hello,
This plugin is not available on the asset store anymore but you can download it from unity.github.com but I dont know if its worth using as it has some issues like the cursor kept flickering and it keeps checking for file changes every second and shows “Listing changed files” message every second on the plugin’s panel.
I looked for a solution to this online and they do have a solution (https://github.com/github-for-unity/Unity/issues/963) which involves using some private developers repo. I also read on the above link that Unity is no longer maintaining this project.
So I am going to keep my life simple and just use Sourcetree.
