Programmers are trained to write code, not read it.

I like to be welcomed when I go somewhere new, and that includes when I visit someone's code. Often all I get is a license statement (which is certainly useful) and then straight into the code.

Sometimes the function names and class names etc are welcoming enough, but often the import of the name doesn't become apparent until I understand the general structure of the code.

So a welcoming comment at the top which outlines what this file of code does and where it fits into the big picture is ... well ... welcoming!