doc: fs examine no longer requires read rights on the volume root vnode

doc: fs examine no longer requires read rights on the volume root vnode

Update the man page to reflect the current access rights required for fs
examine.  Historically, fs examine required read access on the root
vnode of the volume housing the directory or file being examined.  This
access check was relaxed in commit d2d591caf2c9b4cf2ebae708cc9b4c8b78ca5a5a,
since the information returned by the file server is already available
anonymously by other means.

Change-Id: If62b625bce8a260b98fb56a6feec49c674f2de53
Reviewed-on: https://gerrit.openafs.org/12223
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>