PerfCollect install should be more transparent

[davmason]

@brianrob - I ran perfcollect install for the first time yesterday, and it is a rather lengthy install process that does some potentially dangerous things like adding additional feeds to your apt-get sources.

It seems that at a minimum we should give some warning to the user when we suggest running install that it is a lengthy install process with a lot of dependencies. It would also be good to mention that they can either install it through our nice automated process or point them at a list of what needs installed so they can do it manually if they are not trusting of external scripts.