xfconf-plugin: Add readme info contract attributes
- infos/provides = storage/xfconf
- infos/recommends =
- infos/placements = postgetstorage presetstorage
-- infos/status = maintained libc configurable experimental unfinished
+- infos/status = maintained libc configurable experimental unfinished concept limited
- infos/metadata =
- infos/description = storage plugin for xfconf
