Remove --no-site-packages.

It's unlikely anyone is using that old a pip now that we're on wheezy.
Mention pre-requisites from SayIt.

Anyone installing this project will get SayIt installed from the
requirements.txt file and is unlikely to notice the pre-requisites
from the SayIt docs, so I think it's worth repeating them here.
[CL Senate] Small script to import one transcript.