Tweak 'cylc play' resume help.

[hjoliver]

If you use cylc play to resume a paused workflow, currently its says:

Workflow "bug/run101" is already running, listening at "<host>:<port>".

To start a new run, stop the old one first with one or more of these:
* cylc stop bug/run101              # wait for active tasks/event handlers
* cylc stop --kill bug/run101       # kill active tasks and wait

* cylc stop --now bug/run101        # don't wait for active tasks
* cylc stop --now --now bug/run101  # don't wait
* ssh -n "<host>" kill <pid>      # final brute force!

Two minor annoyances with the above advice:

• you don't have to, and may not want to, stop this run before starting another
• there's a blank line in the middle for no apparent reason

On this branch:

Workflow "bug/run101" is already running, listening at "<host>:<port>".

If you like, you can stop it with one or more of the following commands:
* cylc stop bug/run101              # wait for active tasks/event handlers
* cylc stop --kill bug/run101       # kill active tasks and wait
* cylc stop --now bug/run101        # don't wait for active tasks
* cylc stop --now --now bug/run101  # don't wait for tasks or handlers
* ssh -n "<host>" kill <pid>      # final brute force!

This is a trivial change - one review will do.