Add maintainers field and optional dependency description

pkg.info

@@ -1,9 +1,11 @@
 name: xdg-desktop-portal
 description: A portal frontend service for Flatpak and other desktop containment frameworks
 version: 1.20.3
-revision: 4
+revision: 5
 url: https://flatpak.github.io/xdg-desktop-portal/
 license: LGPL2.1-or-later
+maintainers:
+  - [email protected]
 architecture: any
 type: source
 depends:
@@ -17,7 +19,7 @@ depends:
   - pipewire
   - rtkit
 optional_depends:
-  - xdg-desktop-portal-implementation
+  - xdg-desktop-portal-implementation:Required for xdg-desktop-portal to work
 make_depends:
   - docbook-xsl-nons
   - flatpak