Update README.md

Author: financialnoob

README.md

@@ -4,4 +4,5 @@ experiments with portfolio optimization
 substack:
 1. https://financialnoob.substack.com/p/introduction-to-portfolio-optimization
 2. https://financialnoob.substack.com/p/portfolio-optimization-with-weighted
-3. 
+3. https://financialnoob.substack.com/p/portfolio-optimization-random-matrix
+4.