Update README.MD

Author: tboychuk

functional-programming-basics/README.MD

@@ -3,7 +3,8 @@
 This is the tutorial on functional programming basics
 ### Pre-conditions :heavy_exclamation_mark:
 You're supposed to be familiar with OOP, have basic knowledge of JDK, and be able to write Java code. 
-
+### Related exercises :muscle:
+* [Sum of squares](https://github.com/bobocode-projects/java-functional-features-exercises/tree/master/sum-of-squares)
 ### See also :point_down:
 * [Tutorial on Lambdas](https://github.com/bobocode-projects/java-functional-features-tutorial/tree/master/lambdas)
 * [Tutorial on Stream API](https://github.com/bobocode-projects/java-8-tutorial/tree/master/stream-api)
@@ -70,4 +71,4 @@ As you can see there is **no mutable variables** in the second example.
 Now suppose you have enough resources (like CPU and storage), you can try to make you program functional. For instance, 
 instead of updating bank account balance, you can **store each transaction.** When state is required, you can simple 
 apply all transactions. This strategy, where you store transactions and not a state is called [**Event Sourcing**](https://martinfowler.com/eaaDev/EventSourcing.html). It 
-allows you to **avoid concurrent update issues.**  
+allows you to **avoid concurrent update issues.**