You can go to Tools -> Options -> Text Editor -> Snippets. Create a new snippet with your comment.
To insert it into a file just type the name of your snippet and press Ctrl+Space (or whatever shortcut you set for code completion). Voila, your comment is inserted.
Also you can create a licence template but Qt Creator will insert it into .h files too.
Go to Tools -> Options -> C++ -> File Naming. Select there a file with your comment.