Update mailing list details in README.rst

Majordomo commands are no longer used, so update README.rst with the new
method of subscribing to the mailing list.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Link: https://lore.kernel.org/r/20240906211941.850156-1-rebecca@bsdio.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

README.rst

@@ -53,11 +53,10 @@ see REPORTING-BUGS.
 
 An automated mail detailing recent commits is automatically sent to the list at
 most daily. The list address is fio@vger.kernel.org, subscribe by sending an
-email to majordomo@vger.kernel.org with
+email to fio+subscribe@vger.kernel.org or visit
+https://subspace.kernel.org/vger.kernel.org.html.
 
- subscribe fio
-
-in the body of the email. Archives can be found here:
+Archives can be found here:
 
  https://www.spinics.net/lists/fio/