Added matrix exercise

matrix/go.mod

@@ -0,0 +1,3 @@
+module matrix
+
+go 1.22.0

matrix/main.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	a := [][]int{
+		{0, 1, 2},
+		{3, 4, 5},
+		{6, 7, 8},
+	}
+
+	for i := 0; i < len(a); i++ {
+		for _, v := range a[i] {
+			fmt.Printf("%v", v)
+		}
+		fmt.Println()
+	}
+}