chore: remove outdated announcements

Author: Sam Harrison

README.md

@@ -8,9 +8,7 @@
 [![Open Source Helpers](https://www.codetriage.com/sendgrid/sendgrid-csharp/badges/users.svg)](https://www.codetriage.com/sendgrid/sendgrid-csharp)
 
 # Announcements
-**The default branch name for this repository has been changed to `main` as of 07/27/2020.**
 
-* Subscribe to email [notifications](https://dx.sendgrid.com/newsletter/csharp) for releases and breaking changes.
 * Send SMS messages with [Twilio](USE_CASES.md#sms). 
 
 # Overview
@@ -23,8 +21,6 @@ We want this library to be community driven, and Twilio SendGrid led. We need yo
 
 For updates to this library, see our [CHANGELOG](CHANGELOG.md) and [releases](https://github.com/sendgrid/sendgrid-csharp/releases).
 
-Subscribe to email [release notifications](https://dx.sendgrid.com/newsletter/csharp) to receive emails about releases and breaking changes.
-
 We appreciate your continued support, thank you!
 
 # Table of Contents