examples/encryptfield: add an example using go.cloud (#3246)

examples/encryptfield/README.md

@@ -0,0 +1,35 @@
+# Encrypted field example using go.dev
+
+### Setup 
+
+Add the `secrets.Keeper` as a dependency to your project and enable the `intercept` feature flag.
+
+```diff
+func main() {
++	opts := []entc.Option{
++		entc.Dependency(
++			entc.DependencyType(&secrets.Keeper{}),
++		),
++		entc.FeatureNames("intercept"),
++	}
+	if err := entc.Generate("./schema", &gen.Config{}, opts...); err != nil {
+		log.Fatal("running ent codegen:", err)
+	}
+}
+```
+
+### Generate Assets
+
+```console
+go generate ./...
+```
+
+### Update the schema with secret field.
+
+See `ent/schema/user.go` for full example.
+
+### Run Example
+
+```console
+go test
+```