Added some notes on lock ordering.
Added some notes on lock ordering.

They do not yet reflect reality.

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