fix indentation typos in the README.md

Author: afonsograca

Karatsuba Multiplication/README.markdown

@@ -71,12 +71,12 @@ Here's the full implementation. Note that the recursive algorithm is most effici
 
 ```swift
 // Karatsuba Multiplication
-  func karatsuba(_ num1: Int, by num2: Int) -> Int {
+func karatsuba(_ num1: Int, by num2: Int) -> Int {
   let num1String = String(num1)
   let num2String = String(num2)
 
   guard num1String.count > 1 && num2String.count > 1 else {
-  return multiply(num1, by: num2)
+    return multiply(num1, by: num2)
   }
 
   let n = max(num1String.count, num2String.count)