Redirect /getting-started/what-is-warp to home (#3)

The trailing-slash variant /getting-started/what-is-warp/ already
redirects to /, but the no-slash variant returned 404. GSC shows
this URL has 106 clicks and 28,910 impressions over the last 90
days (the highest-traffic 404 in the new docs), so add the no-slash
redirect to match.

Co-authored-by: Oz <oz-agent@warp.dev>

Author: petradonka

vercel.json

@@ -2351,6 +2351,11 @@
       "destination": "/getting-started/supported-shells/",
       "statusCode": 308
     },
+    {
+      "source": "/getting-started/what-is-warp",
+      "destination": "/",
+      "statusCode": 308
+    },
     {
       "source": "/guide/ssh-guide",
       "destination": "/terminal/warpify/ssh/",