When you launch the game hit ctrl-tab and you should see a control panel in the upper left. Click on Achievements in that panel to view them.

If, like me, you have the steam overlay also set to ctrl-tab, the first time will likely have both up at once and be unable to interact with either. In which case, hitting ctrl-tab a 2nd time closes the steam overlay and you can interact with the game's control panel. Hit ctrl-tab a 3rd time to close the control panel and reopen the steam overlay if you want to interact with it. Then a 4th ctrl-tab closes the steam overlay without reopening the control panel.