Update CoC guidance

People getting confused about which page to visit to read the CoC that applies to the project.

Just having link to .NET Foundation one which includes the email address to report issues to.

Made sure that page has a big call out at the top of that page giving appropriate kudos to Contributor Covenant for being awesome. But hopefully it's more clear who to email now.

guidance/readme-guide.md

@@ -39,8 +39,7 @@ You can read [more guidance on the Code of Conduct here](be-nice.md). However, i
 good practice to include the following text somewhere appropriate in your README.
 
  ```
-This project has adopted the code of conduct defined by the [Contributor Covenant](http://contributor-covenant.org/)
-to clarify expected behavior in our community.
+This project has adopted the code of conduct defined by the Contributor Covenant to clarify expected behavior in our community.
 For more information see the [.NET Foundation Code of Conduct](https://dotnetfoundation.org/code-of-conduct). 
  ```