refactor(theme): migrated from website repo

migrated the files required to create the themes
for this mkdocs site.

MR !1 #1

theme-overrides/partials/article_extended_preview.html

@@ -0,0 +1,7 @@
+<a href="{{ page.url|url }}">
+  <span class="twemoji">
+    {% include ".icons/octicons/arrow-right-24.svg" %}
+  </span>
+  Continue reading
+  <hr>
+</a>