Fixed the README callout to the temp dir flag.
Fixed the README callout to the temp dir flag.

For #35.

GoogleCloudPlatform/gcsfuse,BanzaiMan/gcsfuse,mbrukman/gcsfuse,jacobsa/ratelimit,BanzaiMan/gcsfuse,GoogleCloudPlatform/gcsfuse,jacobsa/timeutil,GoogleCloudPlatform/gcsfuse,kahing/gcsfuse