URL Pattern API: mention something about trailing slashes support

[lucacasonato]

MDN URL: https://developer.mozilla.org/en-US/docs/Web/API/URL_Pattern_API

There should be a section in the "Pattern syntax" section (or an example) that describes that trailing slashes are not automatically matched (see whatwg/urlpattern#14).

There should be a mention of how a user can allow trailing slashes: by appending {/}? to their pathname pattern.

cc @wanderview

[wanderview]

FWIW, I tried to explain the reasoning for the chosen behavior here:

whatwg/urlpattern#38 (reply in thread)