Documentation/submitting-patches: Document RESEND tag on patches

Explain when a submitter should tag a patch or a patch series with the
"RESEND" tag.

This has been partially carved out from a tip subsystem handbook
patchset by Thomas Gleixner:

  https://lkml.kernel.org/r/20181107171010.421878737@linutronix.de

and incorporates follow-on comments.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/process/submitting-patches.rst

@@ -346,6 +346,16 @@ that you have sent your patches to the right place.  Wait for a minimum of
 one week before resubmitting or pinging reviewers - possibly longer during
 busy times like merge windows.
 
+It's also ok to resend the patch or the patch series after a couple of
+weeks with the word "RESEND" added to the subject line::
+
+   [PATCH Vx RESEND] sub/sys: Condensed patch summary
+
+Don't add "RESEND" when you are submitting a modified version of your
+patch or patch series - "RESEND" only applies to resubmission of a
+patch or patch series which have not been modified in any way from the
+previous submission.
+
 
 Include PATCH in the subject
 -----------------------------