Update soft-off.md

[GermanG]

Adding Split Peripheral Off On Press basic documentation.

[caksoylar]

I'd like to understand why this setting was implemented and defaulted to first, before encouraging people to turn them off. @petejohanson can you elaborate?

[GermanG]

I think it's related to the issue I reported today #2300

[petejohanson]

I guess I'm confused when you'd ever want to only put the central side into soft off, that you'd need this documented?

[GermanG]

While fixing the peripheral soft_off issue, I noted that the peripheral turned off as soon as I pressed the key, despite the hold-time-ms setting. Upon investigation, I discovered an undocumented option (possibly a workaround for the issue I reported in #2300). After disabling it, I encountered the aforementioned issue. I am unsure of the original author's intent with this option and can only speculate; therefore, I refrained from modifying it. Instead, I documented it and demonstrated what can be done if you prefer to disable it.