Backup archive directory permission settings are missing in the current docs

Build: 7.0.0-3874

Steps:

• Created the directory 'b2' under /mnt folder on the target backup node
• From the UI, used the path '/mnt/b2' for "Create Repo -> Archive" settings.

Observation:

While clicking "Add" button, getting the error message,

Could not add repository: location not accessible by all nodes - node f175cfe76458990c8f989a7cef9b6a93 cannot access location /mnt/b2

After giving "chmod o+wx /mnt/b2", backup repo was created successfully.

Expected info:

Information related to the directory permissions should be present in the docs.

Doc reference: https://docs-staging.couchbase.com/server/7.0/manage/manage-backup-and-restore/manage-backup-and-restore.html

Prints with which the error is observed:

[root@node1-cb601-centos7 mnt]# ls -l

drwxr-xr-x 2 root root  6 Dec 11 10:00 b2