docs(sliceAdd): fix subject

- fix indentation
- fix grammar
- fix packages and import

subjects/sliceadd/README.md

@@ -2,8 +2,8 @@
 
 ### Instructions
 
-- Write a function that takes a slice of integers and int and adds integer in the slice then returns the slice 
-- If the slice is empty, return a slice with the new value
+Write a function that takes a slice of integers and an `int` as arguments, adds the `int` to the slice and returns it. 
+- If the slice is empty, return a slice with the new value.
 
 ### Expected function
 
@@ -15,22 +15,24 @@ func SliceAdd(slice []int , num 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(SliceAdd([]int{1, 2, 3}, 4))
-	fmt.Println(SliceAdd([]int{}, 4))
+	fmt.Println(piscine.SliceAdd([]int{1, 2, 3}, 4))
+	fmt.Println(piscine.SliceAdd([]int{}, 4))
 }
 ```
 
-And its output :
+And its output:
 
 ```console
 $ go run .