update typescript.md in network (Azure#21873)

Author: kazrael2119

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

@@ -15,6 +15,13 @@ typescript:
 typescript:
   package-name: "@azure/arm-network"
   output-folder: "$(typescript-sdks-folder)/sdk/network/arm-network"
+
+directive:
+- from: ddosProtectionPlan.json 
+  where-model: DdosProtectionPlanPropertiesFormat
+  rename-property:
+    from: publicIPAddresses
+    to: publicIpAddresses
 ```
 
 ### Profile: profile-hybrid-2019-03-01