Show which templates/pages a pattern is used on

[thibaudcolas]

From @nicklee in #11,

Overview when viewing patterns showing which templates/pages they are used on (Clearleft’s PL seems to do this, see referenced by on the info tab here: https://patterns.boston.gov/components/detail/address.html)

[thibaudcolas]

Moving this to GitHub Discussions – the idea sounds interesting but it’s unclear how to do this in a reliable way. Thoughts welcome!