Windows: Add comment to AFSInitDirEntry

Change-Id: I6e6164b1dd5c7c8a2c51bcb4cba47667bd343e79
Reviewed-on: http://gerrit.openafs.org/9673
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>