DEV-3183 :add(docs):add subject of concatSlice

subjects/concatslice/README.md

@@ -0,0 +1,40 @@
+## Concat-Slice
+
+### Instructions
+
+- Write a function that takes two slices of integers and returns the concatenation of the two slices. 
+
+### Expected function
+
+```go
+func ConcatSlice(slice1,slice2 []int) []int {
+    
+}
+```
+
+### Usage
+
+Here is a possible program to test your function :
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(ConcatSlice([]int{1,2,3},[]int{4,5,6}))
+    fmt.Println(ConcatSlice([]int{},[]int{4,5,6,7,8,9}))
+    fmt.Println(ConcatSlice([]int{1,2,3},[]int{}))
+}
+```
+
+And its output :
+
+```console
+$ go run .
+[1 2 3 4 5 6]
+[4 5 6 7 8 9]
+[1 2 3]
+```