doc: am --show-current-patch gives an entire e-mail message

The existing wording gives an impression that it only gives the
contents of the $GIT_DIR/rebase-apply/patch file, i.e. the patch
proper, but the option actually emits the entire e-mail message
being processed (iow, one of the output files from "git mailsplit").

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-am.txt

@@ -177,7 +177,7 @@ default.   You can use `--no-utf8` to override this.
 	untouched.
 
 --show-current-patch::
-	Show the patch being applied when "git am" is stopped because
+	Show the entire e-mail message "git am" has stopped at, because
 	of conflicts.
 
 DISCUSSION