Add isEven exercise

After spending so much time having to do bash exercises, writing just
this tiny bit of Go feels incredible

isEven/go.mod

@@ -0,0 +1,3 @@
+module isEven
+
+go 1.23.4

isEven/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strconv"
+)
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Printf("Insufficent arguments:\n")
+		fmt.Printf("Usage: ./isEven 5\n")
+		os.Exit(0)
+	}
+	num, err := strconv.Atoi(os.Args[1])
+	if err != nil {
+		log.Fatalf("Invalid number found: %v\n", err)
+	}
+
+	if s := isEven(num); s == true {
+		fmt.Printf("El número %v es par\n", num)
+	} else {
+		fmt.Printf("El número %v es impar\n", num)
+	}
+}
+
+func isEven(n int) bool {
+	if n%2 == 0 {
+		return true
+	} else {
+		return false
+	}
+}