Fix reference to start_soon() in newsfragment
-Added :func:`cocotb.scheduler.start_soon` which schedules a coroutine to start *after* the current coroutine yields control.
+Added :meth:`cocotb.scheduler.start_soon <cocotb.scheduler.Scheduler.start_soon>` which schedules a coroutine to start *after* the current coroutine yields control.
This behavior is distinct from :func:`cocotb.fork` which schedules the given coroutine immediately.
