Add note that Nodelocal must have a nodeID

[lnhsingh]

An empty nodeID in nodelocal URIs (nodelocal:///) is now banned. You must specify the nodeID (nodelocal://#/)

[lnhsingh]

from dt: "90% of cases, including single-node, you probably want to just use nodelocal://1/ to specify node 1. in like, 9% of cases you might want to pick a specific node — say node 17 is in your region or something. and then in like 1% of cases where you actually have something like NFS setup so the “local” disk on each node is actually some central store, then you might want “self” (nodelocal://self/). so if, say, you’d configured --external-io-directory to point to an NFS-backed directory, instead of doing BACKUP TO 'nodelocal:///nfsmount/backups/x' you would now use BACKUP TO 'nodelocal://self/nfsmount/backups/x'. but I think all our docs examples should feature nodelocal://1/path"