Update appdata.xml

resources/nheko.appdata.xml

 <?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright 2019 mujx, nheko reborn developers -->
 <component type="desktop">
     <id>nheko.desktop</id>
     <metadata_license>CC0-1.0</metadata_license>
@@ -10,10 +11,33 @@
         desktop app for Matrix that feels more like a mainstream
         chat app.</p>
     </description>
+    <translation/>
+    <languages>
+        <lang>de</lang>
+        <lang>el</lang>
+        <lang>en</lang>
+        <lang>fr</lang>
+        <lang>nl</lang>
+        <lang>pl</lang>
+        <lang>ru</lang>
+        <lang>zh_CN</lang>
+    </languages>
+    <content_rating type="oars-1.0">
+        <content_attribute id="social-chat">intense</content_attribute>
+        <content_attribute id="social-audio">intense</content_attribute>
+    </content_rating>
     <screenshots>
         <screenshot type="default">
-            <image>
-            https://dl.dropboxusercontent.com/s/x638uft1fcnybv9/nheko-gnome.png</image>
+            <image>https://nheko-reborn.github.io/images/screenshots/chat-resized.png</image>
+        </screenshot>
+        <screenshot>
+            <image>https://nheko-reborn.github.io/images/screenshots/Start-resized.png</image>
+        </screenshot>
+        <screenshot>
+            <image>https://nheko-reborn.github.io/images/screenshots/settings-resized.png</image>
+        </screenshot>
+        <screenshot>
+            <image>https://nheko-reborn.github.io/images/screenshots/login-resized.png</image>
         </screenshot>
     </screenshots>
     <url type="homepage">https://github.com/Nheko-Reborn/nheko</url>