Installing dd-wrt on a RT-AC56U

I have never used dd-wrt let alone installed it on a device but would like to start. I have an Asus RT-AC56U and have read it has dd-wrt support. I have looked around and cannot find installation instructions for this specific device. Not sure if I have just overlooked it but I would appreciate some help finding installation instructions. 

Looks like this guy in the second post just flashed it from the web gui.

That's the way I've always done it on my RT-N16.

The firmware he links there is old though. Here's the newest one...

I haven't had much luck the last year or two with DD-WRT. Seems like there's always at least one thing I need that's broken. A couple months ago it was the VLANs. No changes in the GUI or telnet/SSH would take effect. So I went back to Tomato and now wish I would of switched sooner. If you're interested, Shibby makes some good builds... Download -