Update changelog for 5.8.0

Author: codejudas

CHANGES.md

@@ -3,6 +3,10 @@ twilio-csharp Changelog
 
 [2017-10-20] Version 5.8.0
 ---------------------------
+**TwiML**
+- Update all TwiML resources with latest changes and parameters *(breaking change)*.
+- Autogenerate TwiML for faster updates and consistency.
+
 **Api**
 - Add `address_sid` param to IncomingPhoneNumbers create and update
 - Add 'fax_enabled' option for Phone Number Search