fix(itoa): student complained for lack of examples

subjects/itoa/README.md

@@ -2,7 +2,7 @@
 
 ### Instructions
 
-- Write a function that simulates the behaviour of the `Itoa` function in Go. `Itoa` transforms a number represented as an`int` in a number represented as a `string`.
+- Write a function that simulates the behavior of the `Itoa` function in Go. `Itoa` transforms a number represented as an`int` in a number represented as a `string`.
 
 - For this exercise the handling of the signs + or - **does have** to be taken into account.
 
@@ -13,3 +13,38 @@ func Itoa(n int) string {
 
 }
 ```
+
+### Usage
+
+Here is a possible program to test your function :
+
+```go
+package main
+
+import (
+	"fmt"
+	"piscine"
+)
+
+func main() {
+    fmt.Println(piscine.Itoa(12345))
+    fmt.Println(piscine.Itoa(0))
+    fmt.Println(piscine.Itoa(-1234))
+    fmt.Println(piscine.Itoa(987654321))
+}
+```
+
+And its output :
+
+```console
+$ go run .
+12345
+0
+-1234
+987654321
+$
+```
+
+### Notions
+
+- [strconv/Itoa](https://pkg.go.dev/strconv#Itoa)

subjects/itoa/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"fmt"
+	"piscine"
+)
+
+func main() {
+	fmt.Println(piscine.Itoa(12345))
+	fmt.Println(piscine.Itoa(0))
+	fmt.Println(piscine.Itoa(-1234))
+	fmt.Println(piscine.Itoa(987654321))
+}