Document ./occ files:scan

[MorrisJobke]

https://doc.owncloud.org/server/8.1/admin_manual/configuration_server/occ_command.html#file-operations

./occ files:scan --help
Usage:
 files:scan [-p|--path="..."] [-q|--quiet] [--all] [user_id1] ... [user_idN]

Arguments:
 user_id               will rescan all files of the given user(s)

Options:
 --path (-p)           limit rescan to this path, eg. --path="/alice/files/Music", the user_id is determined by the path and the user_id parameter and --all are ignored
 --all                 will rescan all files of all known users

[MorrisJobke]

cc @carlaschroder

[carlaschroder]

Thanks @MorrisJobke

[carlaschroder]

#1259