Add example of stack overflow by calling method before end of definition

Author: amirphl

20_struct/03_methods/main.go

@@ -9,6 +9,7 @@ type person struct {
 }
 
 func (p person) fullName() string {
+	p.fullName() // Uncomment this line and see the stack overflow!
 	return p.first + p.last
 }