docs: update documentation link

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

Author: kesselb

README.md

@@ -1,5 +1,5 @@
 # @nextcloud/files
-[![npm last version](https://img.shields.io/npm/v/@nextcloud/files.svg?style=flat-square)](https://www.npmjs.com/package/@nextcloud/files) [![Code coverage](https://img.shields.io/codecov/c/github/nextcloud-libraries/nextcloud-files?style=flat-square)](https://app.codecov.io/gh/nextcloud-libraries/nextcloud-files) [![Project documentation](https://img.shields.io/badge/documentation-online-blue?style=flat-square)](https://nextcloud.github.io/nextcloud-files/)
+[![npm last version](https://img.shields.io/npm/v/@nextcloud/files.svg?style=flat-square)](https://www.npmjs.com/package/@nextcloud/files) [![Code coverage](https://img.shields.io/codecov/c/github/nextcloud-libraries/nextcloud-files?style=flat-square)](https://app.codecov.io/gh/nextcloud-libraries/nextcloud-files) [![Project documentation](https://img.shields.io/badge/documentation-online-blue?style=flat-square)](https://nextcloud-libraries.github.io/nextcloud-files/)
 
 Nextcloud Files helpers for Nextcloud apps and libraries