From: Kyle Lippincott <spectral@google.com>

The documentation says to send an email to majordomo. Doing so gets you
an auto response saying majordomo has been turned down, and to instead
visit https://subspace.kernel.org/vger.kernel.org.html and use the
sub/unsub links.

Update the instructions to reference the supported mechanism for
subscribing to the git mailing list. Include details like these being
mailto links but the subject/body aren't necessary, since it's not
obvious what to put in those fields.

Signed-off-by: Kyle Lippincott <spectral@google.com>

Submitted-As: https://lore.kernel.org/git/pull.1644.git.1705697955144.gitgitgadget@gmail.com