docs: Update license header infos

...to be inline with the SPDX strategy

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

README.md

@@ -80,12 +80,11 @@ All contributions to this repository from June 16, 2016, and onward are consider
 licensed under the AGPLv3 or any later version.
 
 Nextcloud doesn't require a CLA (Contributor License Agreement).
-The copyright belongs to all the individual contributors. Therefore we recommend
-that every contributor adds the following line to the header of a file if they
-changed it substantially:
+The copyright belongs to all the individual contributors. 
+Therefore we recommend that every contributor adds the following line to the [AUTHORS](AUTHORS) file if they made substantial changes to the code:
 
 ```
-@copyright Copyright (c) <year>, <your name> (<your email address>)
+- <your name> <your email address>
 ```
 
 Please read the [Code of Conduct](https://nextcloud.com/community/code-of-conduct/). This document offers some guidance to ensure Nextcloud participants can cooperate effectively in a positive and inspiring atmosphere and to explain how together we can strengthen and support each other.