Merge branch 'docs/local-share-upload' into 'master'

docs: raketasks: Add documentation on uploading to mounted shares

Fog has a local storage provider, which can be use to copy backups to locally mounted cifs / nfs / smb shares. This MR adds documentation to doc/raketasks/backup_restore.md in response to #3387.

@stanhu I found some time tonight and was able to get this started earlier than I initially expected, glad I could contribute.

See merge request !2246