add a new 'overview' MVC example

Former-commit-id: f73cbf6010595c639f6c5b5119e2ec41bc9802a5

_examples/mvc/repository/web/viewmodels/README.md

@@ -0,0 +1,56 @@
+# View Models
+
+There should be the view models, the structure that the client will be able to see.
+
+Example:
+
+```go
+import (
+    "github.com/kataras/iris/v12/_examples/mvc/repository/datamodels"
+
+    "github.com/kataras/iris/v12"
+    "github.com/kataras/iris/v12/context"
+)
+
+type Movie struct {
+    datamodels.Movie
+}
+
+func (m Movie) IsValid() bool {
+    /* do some checks and return true if it's valid... */
+    return m.ID > 0
+}
+```
+
+Iris is able to convert any custom data Structure into an HTTP Response Dispatcher,
+so theoretically, something like the following is permitted if it's really necessary;
+
+```go
+// Dispatch completes the `kataras/iris/mvc#Result` interface.
+// Sends a `Movie` as a controlled http response.
+// If its ID is zero or less then it returns a 404 not found error
+// else it returns its json representation,
+// (just like the controller's functions do for custom types by default).
+//
+// Don't overdo it, the application's logic should not be here.
+// It's just one more step of validation before the response,
+// simple checks can be added here.
+//
+// It's just a showcase,
+// imagine the potentials this feature gives when designing a bigger application.
+//
+// This is called where the return value from a controller's method functions
+// is type of `Movie`.
+// For example the `controllers/movie_controller.go#GetBy`.
+func (m Movie) Dispatch(ctx iris.Context) {
+    if !m.IsValid() {
+        ctx.NotFound()
+        return
+    }
+    ctx.JSON(m, context.JSON{Indent: " "})
+}
+```
+
+However, we will use the "datamodels" as the only one models package because
+Movie structure doesn't contain any sensitive data, clients are able to see all of its fields
+and we don't need any extra functionality or validation inside it.