## CountStars

### Instructions
Write a function called CountStars that counts the stars up to a number given as an argument.
- If the number is negative or equal to 0, return "`No stars`"
- No need to manage overflow.

The Library strconv is allowed.

### Expected Function

```go
func CountStars(num int) string {

}
```
### Usage

Here is a possible program to test your function :

```go
import (
	"fmt"
	"strconv"   
)

func main() {
	fmt.Println(CountStars(5))
	fmt.Println(CountStars(4))
	fmt.Println(CountStars(-1))
	fmt.Println(CountStars(1))
}
```
And its output :


```console
$ go run . 
1 star...2 stars...3 stars...4 stars...5 stars
1 star...2 stars...3 stars...4 stars
No stars
1 star
```