doc: recommend lore.kernel.org over public-inbox.org

Since lore.kernel.org now has the same archive as public-inbox.org and
may have more longevity going forward[1], let's recommend people use it
for finding or referencing messages.

[1] https://public-inbox.org/git/20191120195556.GA25189@dcvr/
      or if you like:
    https://lore.kernel.org/git/20191120195556.GA25189@dcvr/

Signed-off-by: Jeff King <[email protected]>
Acked-by: Eric Wong <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Documentation/MyFirstContribution.txt

@@ -970,7 +970,7 @@ reviewers the changes you've made that may not be as visible.
 You will also need to go and find the Message-Id of your previous cover letter.
 You can either note it when you send the first series, from the output of `git
 send-email`, or you can look it up on the
-https://public-inbox.org/git[mailing list]. Find your cover letter in the
+https://lore.kernel.org/git[mailing list]. Find your cover letter in the
 archives, click on it, then click "permalink" or "raw" to reveal the Message-Id
 header. It should match:
 

Documentation/git.txt

@@ -928,7 +928,7 @@ Reporting Bugs
 Report bugs to the Git mailing list <[email protected]> where the
 development and maintenance is primarily done.  You do not have to be
 subscribed to the list to send a message there.  See the list archive
-at https://public-inbox.org/git for previous bug reports and other
+at https://lore.kernel.org/git for previous bug reports and other
 discussions.
 
 Issues which are security relevant should be disclosed privately to

README.md

@@ -35,7 +35,7 @@ requests, comments and patches to [email protected] (read
 [Documentation/SubmittingPatches][] for instructions on patch submission).
 To subscribe to the list, send an email with just "subscribe git" in
 the body to [email protected]. The mailing list archives are
-available at <https://public-inbox.org/git/>,
+available at <https://lore.kernel.org/git/>,
 <http://marc.info/?l=git> and other archival sites.
 
 Issues which are security relevant should be disclosed privately to