slight improvments

CONTRIBUTING.md

 Max Smietana
+
 Lukas Böhm
+
 Jonas Pfister
+
 Gabriel Denger
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app/templates/About.html

+{% extends "Base.html" %}
+
+{% block page %}
+    <h1>Über</h1>
+    <p>Diese seite ist aus Trauer um Firefox Send entstanden.</p>
+{% endblock page %}
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app/templates/Shared.html

@@ -20,7 +20,7 @@
 
         <script>
             $(document).ready(function() {
-                $("#url").val("{{ url }}");
+                $("#url").val(window.location.origin + "{{ url }}");
 
                 $("#copy-url").click(function(){
                     /* Get the text field */