notes: document cat_sort_uniq rewriteMode

Teach documentation about the cat_sort_uniq rewriteMode that got added
at the same time as the equivalent merge strategy.

Signed-off-by: Jacob Keller <jacob.keller@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1914,8 +1914,8 @@ notes.rewriteMode::
 	When copying notes during a rewrite (see the
 	"notes.rewrite.<command>" option), determines what to do if
 	the target commit already has a note.  Must be one of
-	`overwrite`, `concatenate`, or `ignore`.  Defaults to
-	`concatenate`.
+	`overwrite`, `concatenate`, `cat_sort_uniq`, or `ignore`.
+	Defaults to `concatenate`.
 +
 This setting can be overridden with the `GIT_NOTES_REWRITE_MODE`
 environment variable.

Documentation/git-notes.txt

@@ -331,7 +331,8 @@ environment variable.
 notes.rewriteMode::
 	When copying notes during a rewrite, what to do if the target
 	commit already has a note.  Must be one of `overwrite`,
-	`concatenate`, and `ignore`.  Defaults to `concatenate`.
+	`concatenate`, `cat_sort_uniq`, or `ignore`.  Defaults to
+	`concatenate`.
 +
 This setting can be overridden with the `GIT_NOTES_REWRITE_MODE`
 environment variable.
@@ -368,7 +369,7 @@ does not match any refs is silently ignored.
 'GIT_NOTES_REWRITE_MODE'::
 	When copying notes during a rewrite, what to do if the target
 	commit already has a note.
-	Must be one of `overwrite`, `concatenate`, and `ignore`.
+	Must be one of `overwrite`, `concatenate`, `cat_sort_uniq`, or `ignore`.
 	This overrides the `core.rewriteMode` setting.
 
 'GIT_NOTES_REWRITE_REF'::