To enable the support, run the game with -openvr command line parameter. If no device is found, a dummy one is used. This will cause the game to detect the available oculus devices, select the first one found and launch with a resolution matching the device. For the 1.4.0+ based versions you also need to enable launching applications from Unknown Sources in the Oculus application. To enable the support, run the game with -oculus command line parameter.
Currently the support is available only in the Windows versions of the game.
Experimental support for Oculus API is available in the oculus beta branch on Steam.