Prepare Flatpak release

adjust the appdata file and the build json file to be able to receive a working Flatpak.

data/de.zwarf.picplanner.appdata.xml.in

@@ -3,6 +3,31 @@
 	<id>de.zwarf.picplanner.desktop</id>
 	<metadata_license>CC0-1.0</metadata_license>
 	<project_license>GPL-3.0-or-later</project_license>
+	<name>PicPlanner</name>
+	<summary>Photograph location planning application</summary>
 	<description>
+		This application is designed to calculate the position of the sun,
+		moon and milky way to plan the perfect time to take a photograph.
 	</description>
+	<screenshots>
+		<screenshot type="default">
+			<image>https://gitlab.com/Zwarf/picplanner/-/blob/main/screenshots/picplanner.png</image>
+		</screenshot>
+	</screenshots>
+	<developer_name>Zwarf</developer_name>
+	<update_contact>zwarf@mail.de</update_contact>
+	<url type="homepage">https://gitlab.com/Zwarf/picplanner</url>
+	<url type="bugtracker">https://gitlab.com/Zwarf/picplanner/-/issues</url>
+	<custom>
+    <value key="Purism::form_factor">workstation</value>
+    <value key="Purism::form_factor">mobile</value>
+  </custom>
+	<recommends>
+    <control>keyboard</control>
+    <control>pointing</control>
+    <control>touch</control>
+  </recommends>
+	<requires>
+    <display_length compare="ge">360</display_length>
+  </requires>
 </component>

de.zwarf.picplanner.json

@@ -107,7 +107,7 @@
             "sources" : [
                 {
                     "type" : "git",
-                    "url" : "file:///home/user/Projekte/picplanner"
+                    "url" : "https://gitlab.com/Zwarf/picplanner.git"
                 }
             ]
         }