Mistake/Error email added & gilab repo button added

_config.yml

 # in _config.yml
 title: "Linear Algebra"
-author: 'a team of lecturers and developers from the Delft Institute of Applied Mathematics from the TU Delft University of Technology.'
+author: 'a team of lecturers and developers from the Delft Institute of Applied Mathematics from the TU Delft University of Technology.</br>
+        <div style="font-size:150%;font-weight:bold">Have you spotted a mistake or an error on this page?
+        Click <a id="mailer">here</a> to tell us!</div>
+        <script>
+        var mailer = document.getElementById("mailer");
+        mailer.href = "mailto:openlinearalgebrabook@tudelft.nl?subject=Mistake/Error found at " + window.location.href
+        </script>'
 only_build_toc_files: true
 copyright: "2024"
 
@@ -32,7 +38,7 @@ sphinx:
   config:
     html_theme_options:
       repository_url: "https://gitlab.ewi.tudelft.nl/prime/openlabook-published"
-      use_repository_button: false
+      use_repository_button: true
       logo:
         text: Linear Algebra
         image_light: TUDelft_logo_descriptor_rgb.png