DEV-3414 docs(SliceAdd):add subject

subjects/sliceadd/README.md

@@ -0,0 +1,39 @@
+## sliceadd
+
+### 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
+
+### Expected function
+
+```go
+func SliceAdd(slice []int , num int) []int {
+
+}
+```
+
+### Usage
+
+Here is a possible program to test your function :
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(SliceAdd([]int{1, 2, 3}, 4))
+	fmt.Println(SliceAdd([]int{}, 4))
+}
+```
+
+And its output :
+
+```console
+$ go run .
+[1 2 3 4]
+[4]
+```