Give advice for simplified stat-headline pattern
Give advice for simplified stat-headline pattern

See:
https://github.com/alphagov/govspeak/commit/783a0307190a79a4289b6b8de823
0e583c28c33b

Patterns using `{::` and `{:/` are confusing and lead to errors that
are difficult to spot.

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall