documentation: Add the "files" option to the synopsis of "search --output="

This was inadvertently left off when --output=files was recently added
as a new option.

1 files changed, 1 insertions, 1 deletions

diff --git a/notmuch.1 b/notmuch.1
index 53fa6ffc..2c337497 100644
--- a/notmuch.1
+++ b/notmuch.1
@@ -153,7 +153,7 @@ Presents the results in either JSON or plain-text (default).
 
 .RS 4
 .TP 4
-.B \-\-output=(summary|threads|messages|tags)
+.B \-\-output=(summary|threads|messages|files|tags)
 
 .RS 4
 .TP 4