Updated CONTRIBUTING.md

Author: sergeyklay

.github/CONTRIBUTING.md

@@ -5,7 +5,11 @@ Phalcon Diff is an open source project and a volunteer effort.
 Phalcon Diff does not have human resources fully dedicated to the maintenance of this software.
 If you want something to be improved or you want a new feature please submit a Pull Request.
 
-If you have a change or new feature in mind, please fill an [NFR](https://github.com/phalcongelist/php-diff/wiki/New-Feature-Request---NFR).
+If you have a change or new feature in mind, please fill an [NFR][:nfr:].
+**Note**: We don't add changes directly to stable branches or `master`.
+So, if you are going to do a PR, use the dev-branch.
 
 Thanks! <br />
 Phalcon Team
+
+[:nfr:]: https://github.com/phalcongelist/php-diff/wiki/New-Feature-Request---NFR