Document -logoverwrite and -logappend.

windows/winplink.c

@@ -165,6 +165,9 @@ static void usage(void)
     printf("  -sshlog file\n");
     printf("  -sshrawlog file\n");
     printf("            log protocol details to a file\n");
+    printf("  -logoverwrite\n");
+    printf("  -logappend\n");
+    printf("            control what happens when a log file already exists\n");
     printf("  -shareexists\n");
     printf("            test whether a connection-sharing upstream exists\n");
     exit(1);