DEV-3377 add(docs):add readme for swapFirst

subjects/swapfirst/README.md

@@ -0,0 +1,41 @@
+## swap-first
+
+### Instructions
+
+- Write a function that takes a slice in parameter and swaps the two first element then return the new value 
+- If the slice contains less than two elements return the same slice.
+
+### Expected function
+
+```go
+func SwapFirst(slice []int) []int {
+
+}
+```
+
+### Usage
+
+Here is a possible program to test your function :
+
+```go
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+    fmt.Println(SwapFirst([]int{1,2,3,4}))
+    fmt.Println(SwapFirst([]int{3,4}))
+    fmt.Println(SwapFirst([]int{1}))
+}
+```
+
+And its output :
+
+```console
+$ go run .
+[2,1,3,4]
+[4,3]
+[1]
+```