update and narrow down our "setting up Pants is hard" message
Review Request #1007 - Created Sept. 9, 2014 and submitted
pantsbuild.pants is is a thing. So stop saying it's not installable.
We had commented out stuff about how to install it. Un-comment it.
For a venv-y example, see twitter/commons; not pants' repo, that was only true for a brief time.
BUT, setting up Pants in your code workspace still requires a PhD in Pants-ology. So shift our scary warning over to the setup_repo page.
excellent feedback is excellent.
will merge and publish soon. posting here for the './rbt patch' dance
Revision 2 (+37 -29)