Merge pull request #592 from aydun/patch-2

Update README.md

README.md

@@ -2,8 +2,11 @@
 
 This extension integrates a responsive email template editor, [Mosaico](https://mosaico.io/), with CiviCRM.
 
+If you just want to use this extension, then **DO NOT** download it from here. Instead, 
 View/Download this extension in the [Extension Directory](https://civicrm.org/extensions/email-template-builder).
 
+You only need to download from here if you want to contribute to its development.  Be sure to [read the development documentation](https://docs.civicrm.org/mosaico/en/latest/develop/)
+
 ## Compatibility / Requirements
 * PHP-ImageMagick - recommended.
 * [FlexMailer](https://docs.civicrm.org/flexmailer/en/latest/)