tutorial: cylc broadcast example

[oliver-sanders]

https://github.com/metomi/rose/blame/2018.06.0/sphinx/tutorial/cylc/furthertopics/broadcast.rst#L96

[MetRonnie]

Closed in #38?

https://cylc.github.io/cylc-doc/nightly/html/tutorial/furthertopics/broadcast.html

[MetRonnie]

Or do you mean tackle the TODO

cylc-doc/src/tutorial/furthertopics/broadcast.rst

Lines 89 to 94 in 145fbf4

	It is almost always better for tasks to communicate using files but there are
	some niche situations where communicating via ``cylc broadcast`` is justified.
	This tutorial walks you through using ``cylc broadcast`` to communicate between
	tasks.
	.. TODO - examples of this?

[oliver-sanders]

I think its about the inter-task comms via broadcast, similar to the cylc message further tutorial thinggy.