add typescript.md for deviceregistry (#28690)

Author: kazrael2119

specification/deviceregistry/resource-manager/readme.typescript.md

@@ -0,0 +1,14 @@
+## TypeScript
+
+These settings apply only when `--typescript` is specified on the command line.
+Please also specify `--typescript-sdks-folder=<path to root folder of your azure-sdk-for-js clone>`.
+
+``` yaml $(typescript)
+title: DeviceRegistryManagementClient
+typescript:
+  azure-arm: true
+  package-name: "@azure/arm-deviceregistry"
+  output-folder: "$(typescript-sdks-folder)/sdk/deviceregistry/arm-deviceregistry"
+  generate-metadata: true
+
+```