[Docs] Fix syntax error in nginx code block

docs/admin/01_install.rst

@@ -164,6 +164,7 @@ First, you should get a TLS certificate, e.g. by using `Let's Encrypt`_.
 Then, create a virtual host in nginx, by editing `/etc/nginx/sites-available/aleksis.example.com`.
 
 .. code-block:: nginx
+
    upstream aleksis {
      server unix:///run/uwsgi/app/aleksis/socket;
    }