Anchor links in READMEs don't work on initial page load

[thombles]

I saw a link in a tweet of the following form: https://crates.io/crates/oorandom#user-content-a-brief-history-of-random-numbers

Expected behaviour: Page loads, README loads, JS triggers a scroll to the now-present anchor

Current behaviour: Page loads, README loads, scroll stays at the top, visitor is left wondering what they're looking at

[locks]

Attempted fix at #1848 :)

[thombles]

Amazing, thanks! :)