docs: Fix Trac #10416
Apparently this was broken by b30c6012c7552c874281050d40e5a59012b2c5e7,
but I can't reproduce the issue described there at all.
Signed-off-by: Austin Seipp <email@example.com>
Test Plan: Use my eyes to read the resulting user manual.
Reviewers: hvr, thomie
Reviewed By: thomie
Subscribers: bgamari, thomie
Differential Revision: https://phabricator.haskell.org/D958
GHC Trac Issues: Trac #10416