Tancik/add GitHub button (#624)

* Add github button to docs

* light icon

docs/_templates/sidebar/brand.html

@@ -30,3 +30,18 @@ going well. :) -#}
   >
   {%- endif %} -#} {% endblock brand_content %}
 </a>
+
+<div style="text-align: center">
+  <script async defer src="https://buttons.github.io/buttons.js"></script>
+  <!-- Place this tag where you want the button to render. -->
+  <a
+    class="github-button"
+    href="https://github.com/nerfstudio-project/nerfstudio/"
+    data-color-scheme="no-preference: light; light: light; dark: light;"
+    data-size="large"
+    data-show-cound="true"
+    aria-label="Download buttons/github-buttons on GitHub"
+  >
+    Github
+  </a>
+</div>