Update documentation because we replaced --parallelism with --maximum-concurrent-pieces in the new uplink version

[shaupt131]

Background:

As @littleskunk pointed out, we now need to update documentation because we replaced --parallelism with --maximum-concurrent-pieces in the new uplink version.

NOTE FOR GROOMING: We need to ID what documentation needs to be updated and link it here.

Acceptance Criteria:

Appropriate documentation has been updated

[iglesiasbrandon]

https://docs.storj.io/dcs needs to be updated

[shaupt131]

• https://docs.storj.io/dcs/third-party-tools/file-transfer-performance#downloading-files-with-uplink-cli
  • still mentions --parallelism
• uplink cp --help
  • Still returns --parallelism