Clarified and simplified installation instructions in README

There are a couple changes here (and we can use this pull request to discuss them if necessary). 

* I expanded the acronym FOIA in the first occurrence in case it's not obvious to someone. 
* I added a few notes to the installation instructions based on my setup (in case someone has something similar)
* I removed the add2virtualenv command. I've never needed to use this and the app should run without it. 
* I changed the URL for 'the site should be running at' since the site no longer runs there. 

(Some changes are there because I fixed the long lines).