(occ command) Adds apc.enable_cli instructions

[joshtrichards]

The proper setup of apc.enable_cli is mentioned elsewhere in the manual (for cron and the updater), but not mentioned in the occ command section. Since this triggers an exception, let's help people solve the problem themselves.

☑️ Resolves

• Fix (various) (it's a recurring issue in various repo Issues and the Help Forums)

🖼️ Screenshots

[ChristophWurst]

Screenshots

Please take screenshots of the locally compiled documentation webpage, not the markdown preview. Your Note will look very different in the real documentation.