Complement metainfo.xml

Based on what is already available in the LinuxPhoneApps listing I added some missing metainfo:

Adds vcs-browser url
Adds categories

linux/io.github.polypixeldev.Polypass.appdata.xml

@@ -6,6 +6,11 @@
   <summary>A simple, secure, and easy to use password manager</summary>
   <url type="homepage">https://github.com/polypixeldev/polypass</url>
   <url type="bugtracker">https://github.com/polypixeldev/polypass/issues</url>
+  <url type="vcs-browser">https://github.com/polypixeldev/polypass</url>
+  <categories>
+    <category>Utility</category>
+  </categories>
+
 
   <metadata_license>MIT</metadata_license>
   <project_license>GPL-3.0</project_license>
@@ -69,4 +74,4 @@
       </description>
     </release>
   </releases>
-</component>
+</component>