chore: add funding

This is necessary to add the button to GitHub sponsor at this repository

Signed-off-by: Vitor Mattos <vitor@php.rio>

Author: vitormattos

.github/FUNDING.yml

@@ -0,0 +1,4 @@
+# SPDX-FileCopyrightText: 2025 LibreCode coop and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+github: libresign