Add websocket upgrade to example nginx config.

installation/pleroma.nginx

@@ -19,6 +19,9 @@ server {
     server_name example.tld;
 
     location / {
+        proxy_http_version 1.1;
+        proxy_set_header Upgrade $http_upgrade;
+        proxy_set_header Connection "upgrade";
         proxy_pass http://localhost:4000;
     }
     include snippets/well-known.conf;