[docs] explain ramifications of base path

[dummdidumm]

Closes #4528

On thing I'm wondering is if we should auto-prepend the base path when using goto. This is an API under our control, so we could safe people from prepending it there all the time. It would probably be a breaking change though for everyone who already does this. And it would also probably need an option to turn it off if you actually want to redirect relative to the domain root. So maybe ... don't do this after all?

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