add example

readme.md

@@ -20,6 +20,24 @@ features:
 todo:
  - idk
 
+example: adding some numbers
+
+```
+package main
+import (
+  "log"
+
+	"git.tuxpa.in/a/lambda"
+)
+func main(){
+	arr := []int{1, 2, 3, 4, 6, 5}
+	ans := lambda.Map(arr, func(x int) int { return x + 4 })
+	// ans = []int{5, 6, 7, 8, 10, 9}
+  log.Println(ans)
+}
+```
+
+
 ## parallel
 
 subpackage parallel provides parallelized operations on generic array types