I think beveling is a good option. Select the edges as pictured below, press <kbd>Ctrl</kbd>+<kbd>B</kbd> and drag the cursor in opposite direction to the edges' location. Use <kbd>Mouse Scroll</kbd> to add some divisions. Finally change the rest of the mesh topology to easily add a *Subsurf* and *edge creases*.
[![enter image description here][1]][1]

Here's the final result with a changed topology.
[![enter image description here][2]][2]

And here's the .blend with improved topology: [<img src="https://blend-exchange.giantcowfilms.com/embedImage.png?bid=1117" />](https://blend-exchange.giantcowfilms.com/b/1117/)

  [1]: https://i.sstatic.net/7YniU.gif
  [2]: https://i.sstatic.net/lIILj.jpg