Document how volumes can be mounted into bibigrid's nfs shares manually

[XaverStiensmeier]

This needs to be documented:

I) Start your cluster with a volume (needs to already exist) or a snapshot (a volume will be created from the snapshot) and an nfs share:

masterMounts:
    - test

  nfsShares:
    - test

After cluster creation a nfs shared folder /test exists and the volume test is attached to your instance. The volume is not mounted and not linked to the nfs shared folder at all, yet.

See showmounts --export and lsblk.

II) Mount your volume onto the nfs shared directory /test. For that it needs to be formatted of course. In this example we assume the volume is /dev/vdd.

sudo mount -t ext4 /dev/vdd /test

Now your volume is nfs shared.