base.html.twig doesn't render assets in 'bottom' group

Base template for Learn2 does not render assets from the 'bottom' group. This breaks plugins such as SimpleSearch that adds its JS asset to this bottom group to be executed after the HTML has loaded.

The following snippet, added to `base.html.twig` resolved the issue for me.
```
...
{% block bottom %}
{{ assets.js('bottom') }}
{% endblock %}

```

Open base.html.twig and inspect the existing asset-rendering blocks. Check how the bottom group is handled, then verify that assets.js('bottom') renders the SimpleSearch JavaScript after the HTML has loaded. Done means the bottom-group asset appears in the rendered page without breaking the template.

Written by the indexing model from the issue text.