Documentation update and add some usefull info

[byx01]

Hello!

1. Please update https://postgres.ai/docs/questions-and-answers#what-do-i-need-to-use-database-lab as it now possible to use not only another zfs pool, but also zfs dataset
2. If possible , please add in docs (may be in Tutorial or may be server.yml) some rows how to use several DLE's оn one host ( how to add zfs pool dataset to MounDir , etc) . It was quite difficult to understand for the first time that zfs datasets can be mounted near current zfs pool in MountDir).
   thanks

[NikolayS]

@byx01, thanks for these requests!

1 – will definitely do (but MRs are also welcome, the docs are open too)
2 – might do as well, but this is a lower priority (though again, will be happy to review and accept MR proposals)