docs: Add version-selector in page.html template (#315)

Author: ValerianRey

docs/source/_templates/page.html

@@ -13,4 +13,6 @@
 {% extends "!page.html" %}
 {% block extrahead %}
     <link rel="canonical" href="https://torchjd.org/stable/{{ pagename }}.html">
+    <script src="/version-selector.js"></script>
+    <link rel="stylesheet" href="/version-selector.css">
 {% endblock %}