Google has just released the first build of Android 5.1.1 & a factory image is available now.
The first device which gets Android 5.1.1 is surprisingly the Nexus Player, instead of the Nexus phones, or tablets.
The guys from Android Police did compile a changelog from android-5.1.0_r5 to android-5.1.1_r1. Here you will see some minor updates & fixes, like camera fixes & security bug fixes.
Head over here at Google’s developers website to download this factory image, or other factory images.