feat: use avatar picture variable in metadata

themes/hugo-sustain/layouts/partials/head.html

@@ -12,7 +12,7 @@
           {{- $title = print .Site.Title " | " .Title -}}
         {{- end -}}
     {{- end -}}
-    {{- $image := "/img/profile.jpg" -}}
+    {{- $image := path.Join "/img" .Site.Params.avatar -}}
     {{- if isset .Params "headerimage" }} {{ $image = print "img/" .Params.headerimage }} {{ end -}}
     <meta charset="utf-8" />
     <meta http-equiv="X-UA-Compatible" content="IE=edge" />