Docs: [email protected] has been decomissioned

Update the instruction for subscribing to the Git mailing list
we have on a few documentation pages.

Reported-by: Kyle Lippincott <[email protected]>
Helped-by: Konstantin Ryabitsev <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: gitster

Documentation/MyFirstContribution.txt

@@ -35,8 +35,9 @@ announcements, design discussions, and more take place. Those interested in
 contributing are welcome to post questions here. The Git list requires
 plain-text-only emails and prefers inline and bottom-posting when replying to
 mail; you will be CC'd in all replies to you. Optionally, you can subscribe to
-the list by sending an email to [email protected] with "subscribe git"
-in the body. The https://lore.kernel.org/git[archive] of this mailing list is
+the list by sending an email to <[email protected]>
+(see https://subspace.kernel.org/subscribing.html for details).
+The https://lore.kernel.org/git[archive] of this mailing list is
 available to view in a browser.
 
 ==== https://groups.google.com/forum/#!forum/git-mentoring[[email protected]]

README.md

@@ -39,8 +39,8 @@ Those wishing to help with error message, usage and informational message
 string translations (localization l10) should see [po/README.md][]
 (a `po` file is a Portable Object file that holds the translations).
 
-To subscribe to the list, send an email with just "subscribe git" in
-the body to majordomo@vger.kernel.org (not the Git list). The mailing
+To subscribe to the list, send an email to <git[email protected]>
+(see https://subspace.kernel.org/subscribing.html for details). The mailing
 list archives are available at <https://lore.kernel.org/git/>,
 <http://marc.info/?l=git> and other archival sites.