add themes page on website

docs/_sidebar.md

@@ -3,5 +3,6 @@
 * [Get Started](getting-started.md)
 * [Configuration](config.md)
 * Customization
+  * [Themes](customization/themes.md)
   * [Colors, Background, CSS](customization/css.md)
   * [Create new theme](customization/new-theme.md)

docs/customization/themes.md

@@ -0,0 +1,11 @@
+## flame
+
+![Flame theme](../screenshots/flame.png)
+
+## simplefox
+
+![Simplefox theme](../screenshots/simplefox.png)
+
+## leaf
+
+![Leaf theme](../screenshots/leaf.png)