Find your userSetup.mel file; it should be in Documents > maya > version > scripts (you're on a mac? so it might be different)
Open that file in a text editor (it's just a plain text file)
Copy and paste that text at the end of the document
Save it.

If you don't have that file, create one with that name and paste the text into it. Save it as userSetup.mel in your scripts folder.