docs(bezero): fix subject

- upgrade instructions
- add missing import 'piscine'
- fix indentation

subjects/bezero/README.md

@@ -2,7 +2,7 @@
 
 ### Instructions
 
-- Write a function that takes a slice of integers and returns the same slice by initializing all the elements to 0.
+Write a function that takes a slice of integers as an argument and returns the same slice by initializing all the elements to 0.
 - If the slice is empty, return an empty slice.
 
 ### Expected function
@@ -15,26 +15,27 @@ func BeZero(slice []int) []int {
 
 ### Usage
 
-Here is a possible program to test your function :
+Here is a possible program to test your function:
 
 ```go
 package main
 
 import (
 	"fmt"
+	"piscine"
 )
 
 func main() {
-    fmt.Println(BeZero([]int{1,2,3,4,5,6}))
+	fmt.Println(piscine.BeZero([]int{1, 2, 3, 4, 5, 6}))
-    fmt.Println(BeZero([]int{}))
+	fmt.Println(piscine.BeZero([]int{}))
 }
+
 ```
 
-And its output :
+And its output:
 
 ```console
 $ go run .
 [0 0 0 0 0 0]
 []
 ```
-