Update README.md

README.md

-# User Documentation
+# User Guide aka the Online Help
 
-tbd
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+This repository contains the App Suite Online Help in all supported languages.
+
+Some details:
+- The file format is html
+- The files are generated from the DocBook XML sources files. These source files can be found here:\
+https://gitlab.open-xchange.com/documentation/appsuite
+- The process for building the Online Help is described on this User Documentation Wiki page:\
+https://gitlab.open-xchange.com/appsuite/web-apps/user-guide/-/wikis/0-User-Docu-Startpage/(Process)-Docu-workflow-and-tools
+- The startpage of the User Documentation Wiki can be found here:\
+https://gitlab.open-xchange.com/appsuite/web-apps/user-guide/-/wikis/home