How to add license to an existing GitHub project

1. In your repository, click ‘Create new file’

2.
a) Type ‘LICENSE’, ‘LICENSE.md’ or ‘LICENSE.txt’ as the new file’s file name.
b) The ‘Want to use a new template?’ dialog will appear.

3. Choose your preferred license.

The accepted answer is almost there, but confused me, because it said ‘click the blue plus’ – the interface may have changed – and the image is the same as the OP’s.