Clarify replace disk instructions in Guide
I shut down the NAS to replace the disk to clean the CPU fan and the PSU airways, although the system has AHCI. Item 3 of the replace disk procedure says: "After the disk has been replaced and is showing as OFFLINE, ...". The replaced disk does not show OFFLINE; it shows "UNAVAIL." Moreover, it is no longer identified as adaNp2 (N in [0, 5]); it is identified by a very long radix 10 integer, which is not the gptid. One has to completely guess that this is the replaced disk.
The last sentence of Item 3 says: "After clicking the Replace Disk button, the ZFS pool starts to resilver and the status of the resilver is displayed." That is a true statement, but the resilver status is never updated. The only way to tell if the resilver process is proceeding normally is to type "zpool status <pool>", preferably from PuTTY since OW one loses his place in the Guide. One can wait a long time to figure that out.