* Docs: (subjectively) nicer looking accordion example
the use of `.btn-link` currently just looks a bit odd, subjectively (as in v5 we now force the underline to always be there, while in v4 at least it was only on hover/focus).
`.btn-light` seems more fitting
* Add extra classes for nicer overall look
as suggested by @ysds
* Tweak accessibility note for accordions and optional keyboard interactions