Add motivation

src/semeio/fmudesign/probabilit_idea.md

@@ -4,6 +4,14 @@
 
 ## Background and Motivation
 
+I've been thinking a lot about Monte Carlo analysis the last six months and think I have concluded that a new tool is needed.
+PyMC does not do what we want as it doesn't support Latin Hypercube Sampling, correlations and is slow when there are many variables.
+So, I've started "designing" a new Python library.
+Basically, we need an open source version of the sampling engine tools like @Risk use.
+
+I have not really implemented anything yet, but have instead just started writing down how I'd like such a library to behave and what sorts of features it should have.
+
+The difficult math-stuff was for the most part solved in the last version of fmudesign so what needs to be done is mostly designing a good API.
 
 ### Core Features