paperwork-backend: Add myself to maintainers

Both Paperwork and its backend API are very likely to be updated in par,
but even when not whenever I work on Paperwork I'll check the backend as
well.

Signed-off-by: aszlig <aszlig@nix.build>

pkgs/top-level/python-packages.nix

@@ -6522,6 +6522,7 @@ in {
       description = "Backend part of Paperwork (Python API, no UI)";
       homepage = https://openpaper.work/;
       license = licenses.gpl3Plus;
+      maintainers = [ maintainers.aszlig ];
     };
   };