feat(agents): add some more details on what we want for c++ code

Signed-off-by: Matthieu Gallien <matthieu.gallien@nextcloud.com>

Author: mgallien

AGENTS.md

@@ -49,6 +49,20 @@ Avoid creating source files that implement multiple types; instead, place each t
 - Include a short summary of what changed. *Example:* `fix: prevent crash on empty todo title`.
 - **Pull Request**: When the agent creates a PR, it should include a description summarizing the changes and why they were made. If a GitHub issue exists, reference it (e.g., “Closes #123”).
 
+## c++ Specifics
+
+The following details are important and only relevant when working on the desktop client parts written in c++ language.
+
+You should never use std::iostream for input or output handling and rather use Qt QLoggingCategory and related classes.
+
+All logging categories starts with nextcloud identifier.
+
+Our c++ code is using a pattern known as almost always auto when you should almost always not use explicit data types and rather use the auto keyword.
+
+Our c++ code should can make use of c++ 20 standard features.
+
+We do not use c++ modules and rather use standard include of headers.
+
 ## macOS Specifics
 
 The following details are important and only relevant when working on the desktop client on macOS.