[docs] Add Tentu in the showcase (mui#12122)

* [Showcase] Add Tentu

Add Tentu web app to Discover More > Showcase

* compress image

Author: urkopineda

docs/src/pages/discover-more/showcase/Showcase.js

@@ -202,6 +202,14 @@ const appList = [
     image: '/static/images/showcase/jdupont.jpg',
     source: 'https://github.com/jdupont/jdupont.github.io',
   },
+  {
+    title: 'Tentu',
+    description:
+      'A web app built with Material UI v1 and Firebase that offers the ' +
+      'user news and events of his interest.',
+    link: 'https://tentu.eus/',
+    image: '/static/images/showcase/tentu.jpg',
+  },
 ];
 
 function Showcase(props) {