Add a link to the WebIDE.

Also introduce a translations file for our "textbook" theme.

user/themes/textbook/languages.yaml

+en:
+  THEME_TEXTBOOK:
+    PAGE:
+      FOOTER_NOTICE:
+        CONGRATULATIONS: Congratulations, you've read until the end!
+        EDIT: Edit this course.
+
+fr:
+  THEME_TEXTBOOK:
+    PAGE:
+      FOOTER_NOTICE:
+        CONGRATULATIONS: Félicitations, vous avez tout lu jusqu'au bout!
+        EDIT: Améliorer ce cours.
+
+# es
+# no
\ No newline at end of file

user/themes/textbook/templates/textbook.html.twig

 {% extends 'partials/base.html.twig' %}
 
 {% block content %}
+
     {{ page.content|raw }}
+
+    {% set editor_url = "https://m3p2.ljbac.com/-/ide/project/m3p2/courses/edit/master/-/" ~ page.filePathClean | slice(11) %}
+    <div class="notices blue contribution-incentive">
+        <p>
+            {{ 'THEME_TEXTBOOK.PAGE.FOOTER_NOTICE.CONGRATULATIONS'|t }}
+            &nbsp;&nbsp;&nbsp;&nbsp;
+            <a href="{{ editor_url }}">{{ 'THEME_TEXTBOOK.PAGE.FOOTER_NOTICE.EDIT'|t }}</a>
+        </p>
+    </div>
 {% endblock %}