Add license information for obtain_admin_access_token_element_web.png

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/assets/obtain_admin_access_token_element_web.png.license

@@ -0,0 +1,3 @@
+SPDX-FileCopyrightText: 2022 Julian-Samuel Gebühr
+
+SPDX-License-Identifier: AGPL-3.0-or-later