feat: add vowels-index

subjects/vowels-index/README.md

@@ -13,12 +13,27 @@ func VowelIdx(str string) []int {
 ```
 ### Usage
 
+```go
+package main
+
+import "fmt"
+
+func main() {
+
+	res := VowelIdx("hello Iyan")
+	for _, i := range res {
+		fmt.Println(i)
+	}
+
+}
+```
+And its output :
 ```console
-$ go run . "hello Iyan"
+
-$2
+$ go run . 
-$5
+$ 1
-$7
+$ 4
-$8
+$ 6
-$9
+$ 8
 ```