git-svn.txt: fix usage of --add-author-from

The option '--add-author-from' is used in 'commit-diff', 'set-tree', and
'dcommit' subcommands.

Signed-off-by: Valentin Haenel <valentin.haenel@gmx.de>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-svn.txt

@@ -150,7 +150,7 @@ Skip "branches" and "tags" of first level directories;;
 	dcommit operations), look for the first From: or Signed-off-by: line
 	in the log message and use that as the author string.
 --add-author-from;;
-	When committing to svn from git (as part of commit or dcommit
+	When committing to svn from git (as part of 'commit-diff', 'set-tree' or 'dcommit'
 	operations), if the existing log message doesn't already have a
 	From: or Signed-off-by: line, append a From: line based on the
 	git commit's author string.  If you use this, then --use-log-author