readme: add starting from scratch

[Quoted](http://www.codeofhonor.com/blog/tough-times-on-the-road-to-starcraft) by one of the original engineers of the StarCraft game. 

I think it's very much true for large apps; all too often complete overhauls of apps end up dead in the water, whereas iterating on existing work yields better results. That said, iteration should be possible which automatically leads back to the need of having loose coupling and separating your concerns.

README.md

@@ -39,6 +39,16 @@ The old adage "don't reinvent the wheel" doesn't apply when the wheel comes atta
 
 [Source](http://www.reddit.com/r/programming/comments/1bcebh/programming_best_practices/c9616mn)
 
+#### Don't expect a rewrite to do better than the original
+It's important to remember that when you start from scratch there is absolutely no reason to believe that you are
+going to do a better job than you did the first time. First of all, you probably don't even have the same
+programming team that worked on version one, so you don't actually have "more experience". You're just going to make
+most of the old mistakes again, and introduce some new problems that weren't in the original version.
+
+– Joel Spolsky
+
+[Source](http://www.joelonsoftware.com/articles/fog0000000069.html)
+
 ## Stop Writing Classes
 
 The signature of "this shouldn't be a class" is when the class has two methods, and one of them is the constructor.