add note before picture for easier understanding

README.md

@@ -36,7 +36,7 @@ The author has internalized the project, so there's nothing to think about.
 
 ![Mental Models](/img/mentalmodelsv8.png)
 
-When you onboard new people on your project, try to measure the amount of confusion they have (pair programming may help). If they're confused for more than ~40 minutes in a row - you've got things to improve in your code.  
+When you onboard new people on your project, try to measure the amount of confusion they have (pair programming may help). If they're confused for more than ~40 minutes in a row - you've got things to improve in your code. The more mental models to internalize, the longer it takes for a new developer to deliver value.  
 
 ## Types of cognitive load
 **Intrinsic** - caused by the inherent difficulty of a task. It can't be reduced, it's at the very heart of software development.