If you have a Nexus 7 2013 Wi-Fi, you should check that Update button now, since you may get a prompt to upgrade to Android 5.1. This follows yesterday’s announcement, when Nexus 7 LTE got an OTA as well.
This update brings the device to build LMY470, the same as the LTE model. The update itself measures 170 MB. Just in case the update has not reached your Nexus yet, below you can find the OTA file manual download link you can use to manual sideload.