Learn function decorators with Go

Added snippet about using closures as function decorators in Go. Also
removed a few extra whitespaces.

go.html.markdown

@@ -196,6 +196,21 @@ love:
     learnInterfaces() // Good stuff coming up!
 }
 
+// Decorators are common in other languages. Same can be done in Go
+// with function literals that accept arguments.
+func learnFunctionFactory(mystring string) func(before, after string) string {
+	return func(before, after string) string {
+		return fmt.Sprintf("%s %s %s", before, mystring, after) // new string
+	}
+}
+
+// Next two are equivalent, with second being more practical
+fmt.Println(learnFunctionFactory("summer")("A beautiful", "day!"))
+
+d := learnFunctionFactory("summer")
+fmt.Println(d("A beautiful", "day!"))
+fmt.Println(d("A lazy", "afternoon!"))
+
 func learnDefer() (ok bool) {
     // Deferred statements are executed just before the function returns.
     defer fmt.Println("deferred statements execute in reverse (LIFO) order.")