example: cycle on irregular intervals

[oliver-sanders]

Closes #6336
Requires cylc/cylc-doc#759

Not perfect, but it saves us duping this support.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.cfg (and conda-environment.yml if present).
• Tests are included (or explain why tests are not needed).
• Changelog entry included if this is a change that can affect users
• Cylc-Doc pull request opened if required at cylc/cylc-doc/pull/XXXX.
• If this is a bug fix, PR should be raised against the relevant ?.?.x branch.

[oliver-sanders]

(Code blocks currently render as errors due to a shortcoming in the Cylc lexer)

[oliver-sanders]

(Code blocks currently render as errors due to a shortcoming in the Cylc lexer)

cylc/cylc-sphinx-extensions#86 will fix the issue. That PR needs to be merged & released before this one is (as it will cause cylc-doc build errors otherwise).