5) The "gigantic README" with it's "obscure note" is here http://www.haskell.org/ghc/download_ghc_661.html a few lines away from the download link. You can probably read it in the time it takes you to find and click the download link. Much quicker than waiting for a configure script to detect the problem.
Also, just in case one doesn't know where to look, doing a web search for 'ghc "libreadline.so.4"' gives enough hits to solve the problem. The OP insisisted on compiling from the source (which is OK), instead of using the distributions package (which would have been worked). In this case I expect enough know how to understand what the error message means and being able to install libreadline4. If one hasn't got the know how I expect that one asks nicely ("what can I do / what does that mean") instead of just venting one's frustration in a rather destructive manner ("you bloody program didn't work for me, so I won't use it ever again, there!"). Regards -- Markus