fix: allow docs CI to be manually triggered, better download button (#99)

Author: andreatgretel

.github/workflows/build-docs.yml

@@ -1,5 +1,6 @@
 name: Build docs
 on:
+  workflow_dispatch:
   push:
     branches:
       - main

docs/overrides/main.html

@@ -2,7 +2,7 @@
 
 {% block content %}
 {% if page.nb_url %}
-    <a href="{{ page.nb_url }}" title="Download Notebook" class="md-content__button md-icon">
+    <a href="{{ page.nb_url }}" title="Download notebook" class="md-content__button md-icon" download>
         {% include ".icons/material/download.svg" %}
     </a>
 {% endif %}