add a new 'overview' MVC example

Former-commit-id: f73cbf6010595c639f6c5b5119e2ec41bc9802a5

_examples/mvc/repository/web/middleware/basicauth.go

@@ -0,0 +1,12 @@
+// file: web/middleware/basicauth.go
+
+package middleware
+
+import "github.com/kataras/iris/v12/middleware/basicauth"
+
+// BasicAuth middleware sample.
+var BasicAuth = basicauth.New(basicauth.Config{
+	Users: map[string]string{
+		"admin": "password",
+	},
+})