docs: Update README link to avoid redirection

Author: Sam Harrison

lib/mail/README.md

@@ -10,5 +10,5 @@ php examples/helpers/mail/example.php
 
 ## Usage
 
-- See this complete working [example](https://github.com/sendgrid/sendgrid-php/blob/master/examples/helpers/mail/example.php).
-- [Documentation](https://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/overview.html)
+- See the [example](https://github.com/sendgrid/sendgrid-php/blob/master/examples/helpers/mail/example.php) for a complete working example.
+- [Documentation](https://sendgrid.com/docs/API_Reference/Web_API_v3/Mail/index.html)