This got broken during a move, and the arrows weren't pointing at
anything meaningful. Not sure what the reason for them existing is, but
it's probably better that they be accurate, even if they're still
confusing.

These new docs explain a lot of the current implementation for the BLE
stack, with reference to AN5289 14.1. They also detail the additional
requirements around BLE startup behaviour; specifically, that certain
SYS events must be awaited, and that shci_c2_ble_init should be called.

Since the ble feature is now enabled by default for the docs, the
remaining documentation for the BLE behaviour (as implemented by the
`stm32wb-hci` crate) should be bought in automatically.