add: calculator example to x-tba

x-tba/foundations/calc/01-shortdecl-int-conv/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+func main() {
+	// lesson: multi-return funcs, %v, and _
+
+	a, _ := strconv.Atoi(os.Args[1])
+	b, _ := strconv.Atoi(os.Args[2])
+
+	fmt.Printf("%v + %v = %v\n", a, b, a+b)
+}