tutorial: cylc message

[oliver-sanders]

• Write a tutorial covering cylc message usage. Adding Message Trigger Tutorial to cylc-docs. #105
• Demonstrate a cylc message, cylc broadcast "pipe".

https://github.com/metomi/rose/blame/2018.06.0/sphinx/tutorial/cylc/furthertopics/suicide-triggers.rst#L520

[MetRonnie]

There is a message trigger tutorial: https://cylc.github.io/cylc-doc/nightly/html/tutorial/furthertopics/message-triggers.html

Unless you mean a tutorial on using cylc message manually from the CLI?

Not included is

a cylc message, cylc broadcast "pipe".

[oliver-sanders]

Added in #105.

The broadcast-message pattern is quite important so should be covered somewhere, leaving this open for that.