git-svn: add documentation for --use-log-author option.

Signed-off-by: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-svn.txt

@@ -61,6 +61,10 @@ COMMANDS
 	Set the 'useSvnsyncProps' option in the [svn-remote] config.
 --rewrite-root=<URL>;;
 	Set the 'rewriteRoot' option in the [svn-remote] config.
+--use-log-author;;
+	When retrieving svn commits into git (as part of fetch, rebase, or
+	dcommit operations), look for the first From: or Signed-off-by: line
+	in the log message and use that as the author string.
 --username=<USER>;;
 	For transports that SVN handles authentication for (http,
 	https, and plain svn), specify the username.  For other