is it easy to install self open trunk?
 

something like this

That's not self opening - he hit the button on his key fob. Everyone has that option.

What's really cool in some Audis is the option for Advanced Key to open the trunk/hatch when you come to the back and your hands are full. You'll place your foot under the rear bumper to open the trunk.

The A8 is the only sedan so far that has it.

Auto opening(not unlocking) of the hatch is/was an option on the A4. Retrofitting the motors, etc would be be expensive and difficult.

The 2013 A6 (Prestige) has it as well. However, mine has been very inconsistent (not always working and trunk sometimes pops open on it's own when walking by the rear fender after car is locked). They've disabled all but early 2013's and disabled it in my very early build A6 at my request until there's a fix.

From what I've read, the sensor is on the driver's side so that would make sense.