docs: add new screenshots for appstream + supports

data/io.github.mightycreak.Diffuse.appdata.xml.in

@@ -8,6 +8,11 @@
       Diffuse is a graphical tool for comparing and merging text files. It can retrieve files for comparison from Bazaar, CVS, Darcs, Git, Mercurial, Monotone, RCS, Subversion, and SVK repositories.
     </p>
   </description>
+  <supports>
+    <control>pointing</control>
+    <control>keyboard</control>
+    <control>console</control>
+  </supports>
 
   <metadata_license>FSFAP</metadata_license>
   <project_license>GPL-2.0-or-later</project_license>
@@ -18,8 +23,12 @@
 
   <screenshots>
     <screenshot type="default">
-      <caption>Main window: diff between two files</caption>
-      <image>https://mightycreak.github.io/diffuse/docs/images/screenshot_v0.7.0.png</image>
+      <image type="source">https://mightycreak.github.io/diffuse/docs/images/screenshot_v0.7.7_main_window.png</image>
+      <caption>Main window</caption>
+    </screenshot>
+    <screenshot>
+      <image type="source">https://mightycreak.github.io/diffuse/docs/images/screenshot_v0.7.7_about_window.png</image>
+      <caption>About window</caption>
     </screenshot>
   </screenshots>