I share your excitement. Unfortunately for most of the world, however, both the initial broadcast of "Going Clear" and HBO GO are only available within the United States.
To see (and pass on) this short trailer, I had to access YouTube through a proxy, download the video with a browser extension, and then upload it to my own YouTube account.
HBO currently have no plans to show "Going Clear" in the UK (or, as far as I know, anywhere else).
I will likely be up late after "Going Clear" is Broadcast (we are 5 hours ahead in the UK) scouring torrent and streaming video sites.