Well it's taken me a while to get this far, but I'm finally getting a bit further through the process of installing Web 8. My first attempt had foundered when I failed to accept the installer's defaults - it really, really wants to run the various services on different ports instead of by configuring host headers!

Anyway - this time I accepted the defaults and the content manager install seemed to go OK. (I suppose I'll set up the host header configuration manually at some point once I'm a bit more familiar with how everything hangs together.) So now I'm busy installing and configuring content delivery, and specifically the Discovery service. I got as far as this point in the documentation, where it tells you to run 

java -jar discovery-registration.jar update

This didn't work. Instead I got an error message hinting that perhaps the service ought to be running first. So after a minute or two checking whether I'd missed a step in the documentation, I went to tridion.stackexchange.com and read a couple of answers. Peter Kjaer had advised someone to run start.ps1, so I went back to have a better look. Sure enough, in the Discovery service directory, there's a readme file, with instructions for starting the service from the shell, and also for running it as a service. (This also explains why I couldn't find the Windows service mentioned in the following step in the installation documentation.)

Anyway - so I tried to run the script, and discovered that it expects to find JAVA_HOME in my environment. So I added the environment variable, and but then when I started the script it spewed out a huge long java exception saying it couldn't find the database I'd configured. But... nil desperandum, community to the rescue, and it turned out to be a simple fix.

So with that out of the way, I ran the other script - to install it as a service, and I now have a working discovery service... next step: registration