System Overview: manual chapter feedback and discussion

[anna]

Feedback on the following chapter https://www.phplist.org/manual/ch001_system-overview.xhtml

[kebera]

Typo in upper right corner of online manual:
“DONWLOAD THIS MANUAL”
(Trivial, but disconcerting for new users to see on 1st page.)

[samtuke]

@kebera This has since been fixed; thank you.