Add clarification about state chart versus statechart

[alexhunsley]

StateKit makes use of what it calls a 'state chart'. I presume this not the same as 'statechart', as in the following website/paper?

https://statecharts.github.io/
http://www.inf.ed.ac.uk/teaching/courses/seoc/2005_2006/resources/statecharts.pdf

It might be useful to mention if they are/are not the same thing somewhere high up in the readme about the project. I found this project because I was looking for an iOS statechart library (as per the paper linked above).