Configure IntelliJ IDEA such that source detected in git but Unregistered Vcs root detected

This occurs because Android Studio has detected that you have git projects imported but they have not been "registered" to track their status in Android Studio. Your project will not be negatively affected if you choose not to configure this, IntelliJ only prompts you because it has some integrated version control features that will not be able to function.

So if you want to take advantage of ItelliJ's built in version control options or just get rid of an annoying warning, its an easy fix.

Just register all of the projects you want to have the version control IDE integrations for in the Preferences > Version Control section. You should see this screen:

The UI is a little confusing, but all you need to do is select one of the directories under the Unregistered roots: section and then click the + button in the lower left corner of the window. If you have added all the directories you should see the Unregistered roots: disappear and you should no longer receive this warning.

You can select each directory and use the + and - buttons to determine which projects should use VCS in Android Studio

1. In the error message you have the options "Configure" or "Ignore". Click "Configure".
2. Settings window will open. Click the "Add root" option. In my case I only had one path on the list to choose from. I selected that path. Please see the image I have included below.

3. Click Apply, then click OK.

Look for "Version control" in preferences and set up what VCS should be used:

You have to set this up in order to access function like revert, commit etc from the IDE.

See also, the documentation on Version Control