[IMP] theme_artists: update the theme

This commit updates the theme to improve the design with new colors, new
pictures and new snippet customizations.

task-2580170

Part-of: odoo/design-themes#500

theme_artists/static/description/index.html

@@ -7,7 +7,7 @@
     first projects on the web. Just drag & drop the new building blocks
     you need to easily build your layout. All layouts are made of sections,
     that you can easily combine to fit your specific project.</p>
-    <img src="artists_description.png" class="img-fluid d-block mx-auto">
+    <img src="artists_description.jpg" class="img-fluid d-block mx-auto">
     <hr>
 
     <h2 class="text-muted">Artists Customization Tool</h2>