make doc more mobile-friendly

docs/_templates/layout.html

@@ -1,9 +1,17 @@
 {% extends "!layout.html" %}
 {% block extrahead %}
+{{ super() }}
 <meta name="google-site-verification" content="FNUsDdkOJM9obm9QEdrNBVd9AtAzHzA-aaSMCUrS6C8" />
 <script async defer src="https://buttons.github.io/buttons.js"></script>
 {% if READTHEDOCS %}
 <meta http-equiv="refresh" content="0; URL=https://instaloader.github.io/{{ pagename }}.html" />
 <meta name="robots" content="noindex" />
 {% endif %}
+<style type="text/css">
+div.document { width: 1008px; }
+@media screen and (max-width: 1008px) {
+  div.sphinxsidebar { display: none; }
+  div.document { width: 100%!important; }
+}
+</style>
 {% endblock %}