Improve documentation on configuring NFS mounts

[SiM22]

Will action if/when my PR is merged. Adding so that I dont forget.

NFS mounting is possible. But there is a lack of documentation. This needs adding

[stevenengland]

Hi @SiM22 ,

this role was completely remade in the past month with breaking changes introduced last week.
For more beackground information have a look at:

• Future of this repo? #24
• Relaunch of the Ansible role "paperless-ngx/ansible" #26
• feat: remake of the complete role #27

As a result this issue might be obsolete. To have a clean restart in regards of this role I chose to close existing issues that reference this role before #27 .

--> Feel free to reopen the issue if there is anything I can do for you.

Many thanks for your understanding!