doc: what a patch series is

It seems that we need to clarify that a patch series is a series of related
patches rather than "here are some of my patches as multiple (numbered)
emails."
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/SubmittingPatches

@@ -363,7 +363,8 @@ area or subsystem of the kernel is being patched.
 The "summary phrase" in the email's Subject should concisely
 describe the patch which that email contains.  The "summary
 phrase" should not be a filename.  Do not use the same "summary
-phrase" for every patch in a whole patch series.
+phrase" for every patch in a whole patch series (where a "patch
+series" is an ordered sequence of multiple, related patches).
 
 Bear in mind that the "summary phrase" of your email becomes
 a globally-unique identifier for that patch.  It propagates