On the 20th anniversary of Git, use the "tagline" to link to Discord

There is a new channel on Discord, specifically to celebrate Git's 20th
anniversary (still private, but will be made public in a bit):
https://discord.com/channels/1042895022950994071/1356927327388434564

Let's use the "tagline" (i.e. the fake Git option on the top of the
page) to link to that celebratory channel.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

assets/js/application.js

@@ -138,6 +138,7 @@ var GitTurns20 = {
 
   celebrate: function() {
     document.documentElement.dataset.celebration = 'git-turns-20';
+    $("#tagline").html('<a href="https://discord.gg/UcjvsNQR">--20th-anniversary</a>');
     if ($("#masthead").length) { // only do this on the front page
       (async () => {
         await import('https://cdn.jsdelivr.net/npm/[email protected]/dist/confetti.browser.min.js');